Portraying the Geography of US Airspace with 3-Dimensional GIS-Based Analysis and Visualization

Abstract

The United States identifies, monitors, and defends a vast network of controlled airspaces surrounding its own and allied territories. These controlled airspaces include civilian aviation classes (A through G), drone flying regions, and special use (military) air classifications. These controlled spaces are invisible to the naked eye and often go unnoticed. Managing and portraying data that function in two and three dimensions poses significant challenges that have hindered prior analyses or geovisualizations of controlled airspaces, but we demonstrate here how many of these can be surmounted to visually represent the spatial extent and patterns of US-controlled airspace. In this paper, we demonstrate how these complex spaces can be graphically represented and highlight how cartographic and geovisual representations of often-overlooked domains contribute to a richer understanding of the reach and character of US airspace. The methods described for this work can be extended to other types of multidimensional objects and may facilitate more robust considerations of how Geographical Information Science (GIS) can be useful in analyzing and depicting airspace and territorial claims in three dimensions.

1. Introduction

Analyses of the United States’ territorial reach and global influence frequently highlight its outsized economic authority, its territorial footprint, or its extensive network of military bases and the scope of its military spending [1,2,3,4,5]. Missing from these various perspectives, however, is recognition of a vast expanse of US-controlled airspace that spans and encircles North America and functions as an invisible network that can be monitored and controlled around strategic locations across and beyond North America and into the Pacific Ocean, Arctic Ocean, and Caribbean. Most maps delineating controlled airspace only depict two-dimensional footprints with vertical elements detailed in accompanying data files [6]. Although the sophistication and awareness of remotely sensed imagery has increased dramatically in recent decades, with products such as Digital Globe, GeoEye, and Google Earth moving the view-from-above easily within reach of anyone with access to a smartphone or computer [7], there is almost no readily accessible visualization of how these spaces-from-above exist. The three-dimensional volume of these controlled airspaces has only recently been comprehensively mapped and quantified [8]; for related work in the UK, see [9,10].

This paper attends in new and more expansive ways to airspaces controlled by the US. Extending from prior work that estimated and depicted the temporal volume of US Special Use Airspaces (SUAs) [8], we account here for a fuller and more geographically expansive array of controlled airspace categories. Specifically, we aim to (1) estimate the total volume of US-controlled airspace; (2) identify some of the key challenges that must be navigated in expanding two-dimensional (2D) data to three-dimensional (3D) analyses and projections; (3) effectively portray the scope and character of US-controlled airspaces; and (4) provide an accessible framework to interactively display the geography of controlled airspace that will encourage further research and increase understanding of the significance of this vertical, volumetric dimension of sovereign authority.

Our analysis and geovisualizations include multiple controlled airspaces such as civilian aviation classes (A through G), drone flying regions, and special use military air classifications managed by the US. This broad geographical treatment of controlled airspaces is novel in its own right, but we focus here on methodological challenges, techniques, and responses that allow for a series of interactive representations of airspaces that otherwise remain unseen and too often unnoticed. In particular, we address how to create and graphically portray an interactive platform to depict two and three dimensions of controlled airspaces accessible to a broad set of users.

Previous efforts to translate two-dimensional maps of controlled airspace have predominantly centered around navigating flight paths for civilian air traffic safety or military flights, and require training typically limited either to pilots or air traffic controllers [11,12,13]. Due to the specialization needed to access and portray this information, as well as the simple fact that airspace restrictions tend not to intersect visibly with non-specialists’ daily lives, the vast extent of controlled and restricted airspace has remained largely invisible to most populations living beneath and within the boundaries of these spaces. Considering the tangible and potentially lethal consequences of transgressing these boundaries, making the dimensions of controlled airspace more readily legible remains an important objective.

In the following, we highlight key steps that make it possible to calculate and depict the volume of a large number of airspace boundaries using data maintained by the US Federal Aviation Administration (FAA). This first requires adjusting the FAA-reported lower and upper values to mean sea level (MSL) and accounting for values reported based on height surfaces other than mean sea level (such as surface height or flight level). We then describe how to communicate the volumized airspace and overcome specific challenges that include contending with large geographic dimensions (both planar and vertical) for the entirety of the United States or globe; navigating noise posed by overwhelming and overlapping geographical data, effectively categorizing information layers and enabling users to filter information interactively for display; and constructing additional interactive click-and-zoom-to actions to visualize important but intangible airspace boundaries. This paper presents innovative techniques to estimate and communicate complex 3D geographic information and does so using US-controlled airspace as a particular, significant example.

2. Background

2.1. Vertical Geopolitics and Atmospheric Enclosure

The United States manages extensive networks of controlled airspace above its territory that range in height from a few thousand feet to unlimited or “undefined” altitudes (Ref. [14] notes that unless specified, throughout the paper we use the term “controlled airspace” to include civilian class airspace as well as special use and military airspaces). For much of the Twentieth Century, the application of these extra-territorial airspace claims may have seemed meaninglessly abstract, but with increasingly busy airways and a growing array of surveillance and military technologies now filling the ill-defined domain between “near space” and “outer space”, the vertical geopolitics of airspace is becoming increasingly important in terms of material developments, civilian air traffic, military deployment, surveillance, enforcement, and control [15,16]. The claim of an unlimited vertical dimension to some controlled airspaces also means that its volume is technically infinite. For this analysis, we use the Kármán Line as a reasonable cap to open-ended claims on vertical space, as this is the generally accepted boundary between aeronautical (near), and astronomical (outer) space [17,18,19,20].

Our work to make controlled airspace more visible fits within a broader “volumetric turn” in geography [21] and seeks to redress what [22] describes as airspace operating as a “discrete dimension absent from political maps”. These vertical dimensions of geopolitical claims clearly do matter, even as they remain mostly unnoticed, whether the populations beneath these claims are profoundly impacted by their enforcement or remain largely unaware (see [20,22,23,24,25]). As the “nationalisation of space” [26] continues to take on greater importance, Ref. [16] emphasizes that it is important to reconsider territory not only in terms of two-dimensional areas, but in three-dimensional volumes. The geovisualizations we develop here amply illustrate (see below) that there now exists a far-reaching “atmospheric spatiality” of enclosure that links directly to applications of state power and territorial control [27], see also [28,29].

2.2. Geovisualization, Militarization, and Controlled Airspaces

Dating back to its early formulations, geovisualization has been described as the representation of geospatial information that integrates visual components with computational methods, interfaces with a variety of design elements, and allows users to manage exposure to complex, interactive digital environments [30,31,32,33]. Geovisualization is now widely recognized within the field of Geographical Information Science (GIS). It combines the fundamentals of cartography [34,35], various information visualization channels and methods [36], big spatial data visual analytics [37,38,39], and/or web-based GIS [40,41]. This integration facilitates data exploration, which supports visual thinking, pattern recognition, and hypothesis generation from multiple perspectives [42,43].

Geovisualization techniques and products attend to a diverse array of geospatial phenomena and applications, ranging from architecture and urban planning to sustainable agriculture, public health, outdoor recreation and sport, and crime [44,45,46,47,48,49]. Geovisualizations have also been applied to studies of war, peace, and militarization in the interest of enhancing public understanding of the location, relevance, and character of these important issues [32,50,51], but typically without extending the gaze upwards toward militarized airspaces. The few studies that work to integrate visualizations with airspace, as noted above, focus on details of air traffic safety or flight routes and not how the application of controlled airspace intersects with processes of militarization (e.g., [8,52]).

The United States designates a series of controlled airspace classes to coordinate flights and promote safety and strategic interests on the ground and aloft. Major airspace classes are labeled A through G, a series that goes from more restricted to less restricted as one moves through the alphabet. These alphabetical airspace classes are primarily delineated to accommodate and safely coordinate air traffic surrounding airports and busy air traffic routes. Class A airspace ranges from 18,000 feet above mean sea level to 60,000 feet, an altitude that effectively limits operations to high-performance aircraft operated by commercial carriers or the military. The US’s busiest airports are buffered by the highly restrictive Class B, which requires explicit clearance from air traffic control. Air classes then trend toward decreasing restrictiveness, with Class E only loosely governed, allowing pilots (typically of light aircraft) to navigate via instrument flight rules. Class E airspace also exists above Class A airspace, but we have not included this ultra-high altitude zone, which is effectively bounded vertically only by atmospheric limitations, in our model and calculations. Class G airspace is not controlled and consists of any airspace not covered by any of the more restrictive designations [53].

As Figure 1a illustrates, many of these controlled airspace categories function as stacked columns designed to organize three-dimensional space safely for aircraft and in ways that can be tracked by the US Federal Aviation Administration (FAA). In addition to these broad classes of controlled and uncontrolled (Class G) airspace, there are also Special Use Airspaces (SUAs) that exist as a more specialized (and militarized) set of airspaces with certain characteristics and restrictions. These include Prohibited Areas, Restricted Areas, Warning Areas, Military Operations Areas, Alert Areas, Controlled Firing Areas, and National Security Areas. Each of these SUAs is established around particular security concerns or access limitations that reflect the US national interest. Prohibited Areas, for example, are designated “for security or other reasons associated with the national welfare” [54]. These include some of the most carefully regulated airspaces in the country, including the space above key federal sites in Washington, D.C. such as the White House, Capitol Building, and Naval Observatory (Vice President’s residence). A separate category of SUA, Restricted Areas, mark “unusual, often invisible, hazards to aircraft such as artillery firing, aerial gunnery, or guided missiles”. The FAA warns that entering Restricted Areas without authorization “may be extremely hazardous to the aircraft and its occupants” [54]. Though Special Use Airspaces function as a form of controlled airspace, SUAs differ from Class A through G airspace as they are sometimes transitory, becoming activated or deactivated depending on the movement of particular high-profile individuals (e.g., the US President), activities that rise to the level of a national security interest, or other circumstances that warrant the protection of a column of airspace.

To allow pilots to avoid entering hazardous areas, the FAA provides aeronautical charts for navigation. These maps indicate a variety of airspace categories, including SUAs, designated urban areas that comply with visual flight rules (VFR), and instrument flight rules (IFR) for different categories described above, to assist pilots in navigation [55,56]. However, the maps are two-dimensional and can be quite confusing for non-specialists due to a significant amount of overlapping information, as depicted in Figure 1b.

3. Research Methodology

This section outlines our GIS-based analysis and visualization methodology developed in this study to effectively illustrate the geography of US airspace and achieve the four specific objectives presented in the introduction. The overall workflow is presented in Figure 2 below and consists of several key steps:

1. Collecting publicly available airspace data.

2. Processing and analyzing these data to calibrate airspace heights and estimate their volumes.

3. Publishing the processed data as web-based hosted feature and map services using ESRI’s ArcGIS Online platform. All the backend data are maintained on the cloud and managed by our ESRI’s Online server license.

4. Developing a standalone web-based interactive visualization platform that utilizes the data from the hosted feature services, along with cartographic designs and web designs created with HTML, CSS, and the ESRI JavaScript API.

5. Hosting the visualization platform on a GIS enterprise server located at the University of Colorado-Colorado Springs for public access.

The following Section 3.1 and Section 3.2 offer a comprehensive overview of our data collection process, the characteristics of publicly available airspace data, and our methods for height calibration and airspace volume estimation. Furthermore, we will describe the development of our visualization platform and discuss the key challenges we encountered, along with the solutions we developed for effectively visualizing three-dimensional airspace in Section 3.3.

3.1. Airspace Data

Data for the US airspace were downloaded as GIS shapefiles from the FAA open data site (https://adds-faa.opendata.arcgis.com/ accessed on 16 June 2021) covering a representative eight-week period from 17 June 2021 to 2 August 2021. This study focuses on three major airspace categories: Special Use Airspace (SUA), Class Airspace, and Boundary Airspace.

Each airspace object in this FAA dataset is represented as a two-dimensional polygon indicating its footprint on the earth’s surface. In the context of geographic information, each polygon is a closed shape defined by a connected sequence of x and y coordinate pairs, where the first and last coordinate pairs are the same and all other pairs are unique. The data comprise a polygon record for each airspace object within the categories listed in

Table 1. Airspace categories and corresponding object quantity.

Categories	Type Code	Description	Count (Polygons)
Special Use Airspace (SUA)	P	Prohibited Area	15
	R	Restricted Area	605
	D	Danger Area	22
	A	Alert Area	39
	W	Warning Area	210
	ADA	Advisory Area	45
	ADIZ	Area Defense Identification Zone	13
	MOA	Military Operation Area	692
	DEF	National Defense Area	8
	SATA	Special Airspace Terminal Area	39
Class Airspace (with a specified class)	A	Class A	89
	B	Class B	411
	C	Class C	386
	D	Class D	628
	E	Class E	4447
	F	Class F	33
	G	Class G	15
Other Boundaries	BZ	Buffer Zone
	CTA	Control Area
	CTR	Control Zone
	MODE-C	Mode-C Transponder Area
	TMA	Terminal Control Area
	TMA-P	Part of a Terminal Area
	ACC	ACC—Area Control Area
	TMA	TMA—Terminal Control Area
	OCA	OCA—Oceanic Control Area
	UTA	UTA—Upper Control Area
	ADIZ	Area Defense Identification Zone
	ARTCC	Air Route Traffic Control Center
	CTA	Control Area
	CTA-P	Part of a Control Area
	FIR	Flight Information Region

. The two-dimensional polygons from different categories may overlap depending on their geographical locations and spatial extents.

The data attributes of these polygons indicate the lower and upper vertical restrictions for flying. These vertical restrictions are expressed relative to either Mean Sea Level (MSL), Above Ground Level (AGL), or Flight Level (FL). Figure 3 provides an example of the polygon data model, showcasing the prohibited airspace above the US National Mall and Memorial Parks.

The downloaded data contain 7785 polygon airspace objects along with their associated attribute data. These objects cover a total footprint of 72,395,213 square miles of land and sea surface area both within and beyond the US border. Table 1 provides a summary of the available airspace, with categories distinguished by type codes and their respective count.

Figure 4 displays the two-dimensional (2D) maps for each airspace category: Special Use Airspace (SUA), Class, and Boundary. These maps use color and line thickness to represent different subcategories of airspace and their upper height limits. Some airspace objects have no vertical restrictions, meaning there is no upper limit. As noted above, these are capped at the Kármán line at 330,000 feet above mean sea level (MSL) in this study. These maps exemplify traditional 2D static mapping techniques. Although they effectively represent horizontal geographic dimensions, they are limited by not conveying vertical dimensions and do not support interactive exploration for users.

3.2. Calibrating Airspace Vertical Restrictions and Estimating Airspace Volume

The first step in our data analysis involved calibrating the vertical restrictions for each airspace. These restrictions are defined by lower and upper bound limits, which are based on different height reference surfaces, specifically Mean Sea Level (MSL), Above Ground Level (AGL), or Flight Level (FL). In this study, we adjusted these vertical limit values, so they are all referenced to Mean Sea Level. This calibration is essential for accurately mapping airspace objects in three-dimensional space and is also necessary for estimating the volume of each airspace object for reporting purposes.

For this task, it is essential to determine the surface elevation relative to the Mean Sea Level (MSL) for each airspace footprint polygon. Although digital elevation model (DEM) data from the US are freely available, collecting these data for the entire study area is impractical due to their large size. Additionally, the airspace footprints in this study are not continuous but consist of discrete polygons that vary in size; a larger polygon may encompass areas with significantly varying surface elevations.

To address this issue, we divided each airspace footprint polygon into 100 equal-area segments (see Figure 5). We then estimated the surface elevation for the centroid of each segmented polygon. We utilized the Python API provided by the USGS National Map [57] to gather elevation data for these centroids. The code was designed to request elevation data from the server every 20 s after disconnecting, allowing us to manage the large dataset and frequent server interruptions effectively.

The next step in our analysis was to estimate the three-dimensional volume of the airspace objects reported during the analysis period. To determine the volume of each object, we first calculated its total vertical extent using the calibrated lower (l) and upper (u) vertical boundaries. The volume, $v$, for each airspace object is calculated as follows:

$$v=A\times (u-l)$$

(1)

where A is the base area in square miles, $u$ is the upper bound vertical restriction in miles w.r.t. MSL, and $l$ is the lower bound vertical restriction in miles w.r.t MSL. ArcGIS Pro version 3.2.0 [58] software was used to visualize the airspace objects, estimate the footprint polygon area, and perform volume calculations.

3.3. Constructing Visualization Platform

3.3.1. Motivations and Objectives

The volumized airspace analyzed in this project serves as a compelling example of complex 3D geographic information. Its significance and complexity are reflected in numerous characteristics, including (1) a large data quantity with overwhelming footprint overlaps, (2) a wide range of categories subjected to specific vertical bounds for flying restrictions, (3) a substantial variation in size with a footprint area ranging from less than 1 to approximately 55 million square miles, and a volume ranging from less than 1 to approximately 3.4 billion cubic miles, and (4) an expansion on a significant geographical area.

Effectively conveying this complex 3D airspace information through maps and visualizations poses significant challenges. It is essential to leverage visual channels and tools to enhance viewers’ understanding of the spatial distributions and patterns of airspace across different geographical scales. This necessitates careful consideration of how to visually represent data through thoughtful design and clear communication, ensuring that it is accessible and comprehensible for the audience. It is also important to engage the audience as individuals who may be unfamiliar with airspace concepts or GIS. Additionally, facilitating their interactive visual discovery in connection with a familiar geographical context, whether through specific terrain surfaces or urban settings viewed in 2D maps, can greatly enhance their experience and understanding.

Traditional mapping techniques that use a single static 2D or 3D view have limitations when it comes to representing complex 3D information. Each map only provides a fixed perspective, which can restrict user engagement. While maps of multiple small static views or animations can offer various viewpoints, they still fall short in promoting user interaction. This includes the ability for users to adjust the zoom level, change camera angles or tilts, and select an individual or groups of objects to view.

In this paper, we utilize ESRI ArcGIS Online [59] along with HTML, CSS, and JavaScript (HTML/CSS/JS) web programming languages to create a standalone visualization platform that interactively portrays US airspace. The platform is hosted on our GIS enterprise server located at the University of Colorado-Colorado Springs and is publicly accessible. The product can be found at https://gishub.uccs.edu/USAirspace/, accessed on 16 June 2021. The code used to develop this platform is available in the Supplementary Files. The primary goal of this platform is to utilize GIS visualization techniques, such as visual channels, data filtering, and interactive features, to help users explore the geographical extent and patterns of US airspace through a simple yet effective user interface design.

Interactive GIS web maps and applications, such as story maps, have been present in the GIS field for some time [60]. However, when lacking customization, it can struggle to map large and complex 3D geographical information such as airspace, as discussed in this study. The solution presented here is a customized version of ESRI’s GIS web scenes and apps. Screenshots demonstrating the platform in action can be found in various figures presented in Section 3.3.3. below. Our visual platform enhances user interaction, making it easier for the audience to navigate extensive geographic dimensions (both horizontal and vertical) and manage the overwhelming and overlapping geographical data. We achieve this through effective 3D data modeling, effective cartographic designs, and interactive user panels for information categorization and filtering, as well as by providing connectivity between 2D and 3D perspectives through additional interactive click-and-zoom actions.

3.3.2. Visual Design

The visual design of our airspace visualization platform is based on key principles of data visualization [34,36] and adopts an innovative approach to effectively present complex 3D information in a simple and user-friendly interactive way. Data visualization principles typically emphasize the use of basic geometric shapes—such as points, lines, areas, polygons, and volumes—to represent items and their relationships. Visual channels, including position, color, size, shape, and arrangement, help to distinguish different categories and indicate the magnitude of various attributes.

In this study, each airspace object is visualized on our platform using a multi-patch mark type. In the field of geographic information science, a multi-patch is a 3D geometry that represents the outer shell of a 3D object. Here, each multi-patch represents the vertical boundary of the airspace, essentially forming its exterior vertical shell [61]. Unlike volumes, multi-patches do not include the exterior horizontal shell. This design choice prevents the footprint polygon from overlaying and obscuring the Earth’s surface when viewed from a top-down perspective. This data model is particularly effective for visualizing airspace, as it maintains a clear visual connection between the 3D airspace volume and the 2D surface map, even when the viewing camera is rotated or tilted at various angles. When combined with enhanced interactive features in our visualization platform, this model effectively illustrates crucial yet often intangible airspace boundaries.

Our design incorporates several visual channels, particularly position and color, as well as the size and shape of airspace objects, to effectively represent the geographical patterns of airspace and their magnitudes in three-dimensional space. Each airspace object in our platform is mapped to its geographic location using latitude, longitude, and height, based on the WGS84 Web Mercator coordinate system [62]. This mapping reveals the dimensions of each object’s two-dimensional footprint and three-dimensional volume. Additionally, the vertical extent of the airspace is represented by the height of the multi-patch. We offer an option to exaggerate the vertical height, increasing the vertical size of the multi-patch if a user desires, to enhance visualization.

The color channel is carefully optimized to indicate different airspace categories, utilizing color hues based on established mapping design principles [34]. We use gold to represent general airspace, black for prohibited airspace, red for restricted and danger zones, red-orange for alerts and warnings, yellow for advisory zones, green for military and defense areas, and pink for special traffic monitoring. Our color coding for aviation airspace classes aligns with the conventions used in FAA charts for class airspace designations, as illustrated in Figure 1.

Our visualization platform displays airspaces across the entire globe using ESRI’s global web scene application [62]. A significant advantage of using ESRI’s global web scene is its adaptive mapping scale, which adjusts based on the user’s zoom levels while interacting with the display [63]. The zoom levels range from 0 (global view) to 23 (very detailed view), with each level corresponding to a specific scale on the map. For instance, the 0 zoom level is equivalent to the scale of 1:70.5310735, while the 23 zoom level corresponds to 1:591,657,527.591555. This allows users to adjust the display’s level of detail by zooming in or out. As the zoom level increases, the scale also increases, enabling more detailed observations of the airspace domain in three dimensions, along with a visual connection to the Earth’s surface and surrounding landmarks.

To address the significant overlap of airspace objects, we have implemented display filters in our platform that enable users to perform temporary data queries. These filters help limit the categories of airspace objects that are displayed. Users have the option to interactively enable or disable these filters, as explained in more detail in the following subsection.

3.3.3. Interactive Functionalities

The platform interface, as shown in Figure 6, consists of two main panels. The panel on the right side offers interactive data filtering options, allowing users to select one of three primary airspace categories: SUA, Class, or Boundary. There is also an option to hide all airspace data. Users can then explore visualizations for each selected subcategory within the main categories or choose a combination of them. The left panel serves as the primary display window for the selected data. The navigation functions located on the left side of this display panel allow users to interact with the visualizations. These functions include zooming in (), zooming out (), panning the view in different directions (), rotating the view at various angles (), aligning the view to the north (), and returning to the default display ().

We have processed our data to calibrate vertical height restrictions (both lower and upper limits) to Mean Sea Level (MSL). Consequently, our visualization accurately maps the airspace boundaries using true vertical measurements. However, due to the extensive geographical area covered, vertical boundaries extending up to the Kármán line appear relatively low. To improve the visualization, we have implemented an option to toggle the display of vertical exaggeration on or off. Figure 7 shows a static view of the main display with and without this option.

Figure 8 and Figure 9 illustrate how users can interact with the visualization, enhancing the information discovery process. The first option is to enable the display of a highly interactive table listing all available airspace boundaries to browse when the user selects only one subcategory of SUA or Class to display. When the “Show Detail Boundary List” option on the top right corner of the main display is activated, as shown in Figure 8, it displays all airspace boundaries in a table format for user interaction. Users can click on each listed airspace boundary to select and then choose the “zoom-to” option located at the end of the table record. The system will automatically zoom in on the selected boundary within the main display. Users can follow a sequence of select-and-zoom actions to examine each boundary thoroughly. For each selected boundary, additional information—such as height limits, footprint area, and volume—can be accessed via an information popup. Users can also click the “zoom-to” function within this popup to adjust the camera view, allowing a direct top-down perspective of the Earth’s surface from the selected airspace. This interactive option is demonstrated in Figure 9. Overall, this capability connects the user’s 3D and 2D viewing perspectives, effectively bridging the intangible 3D airspace with a more familiar 2D map of the Earth’s surface.

4. Discovering the Geography of US Airspace

This section presents and discusses key findings from our observations using the developed platform. Due to the limitation of only being able to display our maps in a static format for publication, we have included several static maps that illustrate and communicate the observed geography of US airspace, along with its spatial distribution and patterns. However, these maps provide only snapshots of the main display obtained while interacting with the platform. We encourage readers to explore the interactive platform at https://gishub.uccs.edu/USAirspace/, accessed on 16 June 2021.

The geographical extent of US airspace is quite vast, as illustrated in Figure 10. This expansive area encompasses US territories and those of its neighbors, extending eastward over much of the Pacific Ocean, including regions belonging to certain US allies. The total area covered by US airspace is approximately 72,395,213 square miles, as estimated in this study by determining the minimum bounding polygon that outlines all airspace boundaries. Additionally, the total volume of US airspace, as presented in Figure 10, is estimated to be approximately 12,555,200,000 cubic miles, calculated by determining the minimum bounding volume that encompasses all claimed US airspace objects.

Figure 11 clearly illustrates the airspace boundaries connected to countries with intersecting land areas. In North America, the United States controls the airspace above its entire territory, extending this control to its immediate neighbors, Canada and Mexico. This authority also encompasses parts of the Caribbean, including areas like Cuba and the Bahamas.

Moreover, the United States claims control over the airspace of its overseas state, Hawaii, as well as its unincorporated territories Navassa Island and Puerto Rico in the Caribbean, and American Samoa, Guam, the Republic of the Marshall Islands, the Federated States of Micronesia, the Commonwealth of the Northern Mariana Islands, and the Republic of Palau in the Pacific Ocean.

It is important to note that the US has also expanded its airspace claims over areas of or near various allies, covering a significant portion of the Pacific. This includes partnerships with Australia, New Zealand, Japan, and the Philippines, as well as territories in Indonesia, Papua New Guinea, and smaller nations in Oceania such as Kiribati, Nauru, Vanuatu, and the French overseas territory of French Polynesia. The observed pattern here reflects a collaborative approach that strengthens international relationships, enhances regional security, and extends the reach of the US-regulated airspace.

Figure 12, Figure 13 and Figure 14 illustrate the geography of Special Use airspace regulated by the United States. As mentioned, this category is established based on specific security concerns and access limitations that reflect national interests. In this study, given its connection to defense and security, we merged the Area Defense Identification Zone data collected from the US airspace boundary dataset with Special Use airspace data for visualization. Figure 11 shows continuous protective barriers with no upper height restrictions surrounding the entire continental United States, Canada, Cuba, and two major US territories—Hawaii and Guam. It is also noteworthy that similar barriers are established around the large Philippines island of Luzon, home to several large US military bases.

Figure 13 provides a detailed map of the SUA subcategory airspace distribution within these protective barriers. These airspace dimensions come with restrictions and warnings for nonparticipating aircraft, indicating potential danger or conflicts with participating activities. Some SUA airspaces have permanent restrictions, while others are temporary. However, as mentioned previously, our study here focuses on visualizing all these airspaces during the data collection period to provide more clarity. The visualizations shown in Figure 13a highlight restricted areas (dark red), danger areas (bright red), alert areas (peach), and military operation areas (dark olive), which are mostly strategically related to US military bases and/or cooperating national security interests (e.g., with Canada). In this figure, we highlight several representative restricted airspaces, numbered 1 to 9. These include a cluster of airspace objects in southwestern British Columbia surrounding Canada’s 19 Wing Operations (#1), Vandenberg Air Force Base (#2), Creek Air Force Base and the Nevada National Security Site (#3), Naval Air Weapons Station China Lake (#4), Wendover Air Force Base (#5), Holloman Air Force Base, White Sands Missile Range, and Fort Bliss (#6), Cape Canaveral Space Force Station (#7), Air Traffic Management Station R-6604 (#8), and US Army Aberdeen Proving Ground (#9).

Additionally, Figure 13a,b display eight national defense airspaces marked with temporary flight restrictions (TFR) in dark green. These airspaces are activated when necessary and include two national defense airspaces at Grand Forks Air Force Base in North Dakota, the national defense airspace at Beale Air Force Base in California, the Dallas national defense airspace in Texas, the San Angelo national defense airspace in Texas, the Macon national defense airspace in Georgia, the Libby Army Airfield national defense airspace in Arizona, and the Finegayan national defense airspace in Guam. Furthermore, Figure 13 shows a clear distribution of warning airspace marked in dark orange. A distinct pattern is observed along the US coast, extending three nautical miles outward from the land.

One subcategory that was not shown clearly in Figure 13, because of its low altitude upper limit values compared to those of other subcategories, is prohibited airspace. We map these separately in Figure 14 with an additional 50 times vertical exaggeration to enhance visual performance and provide a detailed list of airspace names and locations. Included in this subcategory are airspaces above landmarks subject to the most stringent US protection.

Our earlier research [8] established a framework for mapping the SUA airspace as a separate category, focusing on its volume estimation with temporal changes. In this study, we have extended from that work by incorporating advanced visualizations that illuminate these often abstract geographic entities, making them more accessible and understandable to a wider audience. This visual enhancement serves not only to engage non-specialists but also to vividly illustrate the dedicated efforts of US government agencies and military operators. Their work aims to create a robust and intricate protective network, ensuring safety and security both on the ground and within the airspace overhead.

Figure 15 illustrates the geographic distribution of the different class airspace categories. The pattern observed indicates that the boundaries of the class airspace, especially between Class B to G, are densely packed, encompassing the airspace over the contiguous United States, Alaska, Hawaii, Guam, and American Samoa. This illustrates how civilian airspace has been carefully established for effective and safe operations for decades. The spatial distribution of Class A airspace, recognized as the most tightly controlled class airspace, is especially extensive. This category is marked distinctly in red, highlighting its broad range and significance within the class airspace system. While Class A airspace is not militarized in the same way SUAs are, the careful regulation of these high altitude zones ensures the safe operations of specialized aircrafts that can fly at these altitudes. This regulation also illustrates the extensive global reach of US-controlled airspaces.

It is essential to recognize that the visualizations presented in the figures above capture various instances of our dynamic and interactive views accessed through our developed visualization platform. The results of this work extend beyond the examples presented here. For instance, while using the visualization platform, users can access several interactive options. These include the ability to zoom into each airspace boundary, adjust the viewing angle with a single click to switch between 2D and 3D perspectives, display information pop-ups, take a boundary-by-boundary tour through the list of available airspace boundaries, and experience visualizations with or without enhancement using a vertical exaggeration. While we cannot effectively illustrate these additional features dynamically within the paper, they can be fully experienced by exploring the system itself (located at https://gishub.uccs.edu/USAirspace, accessed on 16 June 2021).

Our visual-based information system developed in this work successfully portrays the complex three-dimensional structure of airspace. For the first time, it enables non-specialists to observe and comprehend the spatial distribution and expansion of airspace more effectively. This work establishes a foundation for accurately mapping the geography of airspace, making this rich and valuable geographic information more accessible. Ultimately, this advancement will support and enhance understanding at both individual and organizational levels, fostering greater knowledge and collaboration in the field.

5. Discussion and Conclusions

Controlled airspaces are characterized by qualities that make them both particularly challenging and particularly important to identify, analyze, and visualize. The jurisdictional boundaries applied to airspaces are effectively invisible, whether to people gazing up at the sky or those looking at two-dimensional maps of airspace designations trying to cast those vertically into three dimensions. Despite their invisibility, however, many controlled airspaces also exist as strictly enforced material spaces that are under constant surveillance. The temporal inconsistency of certain controlled airspaces adds an additional challenge in coming to terms with them, as some reflect a steady assertion of national security interests and US spatial control while others are activated and deactivated depending on time of day, day of the week, or certain events or conditions (such as travel and other activities by the US President, Vice President, or other protected individuals). In order to be comprehensively rendered, controlled airspaces would need to be portrayed across four dimensions, a standard that static representations have struggled to meet but one that is newly feasible using digital interfaces and GIS (see [8]).

In this paper, we have limited our scope to three dimensions in order to create as clear, streamlined, and useful interface as possible to visualize US-controlled airspaces as they exist across and above the surface of the Earth. Creating and portraying geovisualizations of controlled airspaces in three dimensions still presents an array of challenges as the US manages airspace across vast expanses of North America, portions of the Caribbean, and a broad archipelago spanning significant portions of the Pacific. These airspace claims vary in height, and therefore volume, in ways that make scaling and effective visualization—as well as measuring their extent—difficult or impossible. For some of these cases, the height (and thus volume) of controlled airspace is unlimited; as noted above, in order to depict and quantify the extent of these infinite spaces, we have capped unbounded airspaces at the Kármán Line. Even with this vertical limit imposed, the three-dimensional map of controlled airspace reveals heights ranging from a maximum of 700 feet above ground level to others extending to the 330,000 foot cap of the Kármán Line, creating graphical challenges to any three-dimensional representation that covers a significant portion of the Earth and a variety of vertical dimensions. Some air spaces also start at a fixed altitude above ground level, creating a complex set of overlapping layers as one moves from the Earth’s surface upwards.

In order to respond to these graphical challenges, the 3D interactive visualization platform we developed includes rapid scaling and zooming capability, optimizing the user view interactively with camera angle and tilt adjustment, a linkable and interactive table-based list, amplification of low-lying controlled airspaces to make them more apparent, and metadata that can be easily clicked to indicate precise dimensions of each airspace polygon.

One important benefit of the 3D interactive model we provide is that the scope and location of US-controlled airspaces for the first time become evident. By utilizing the 3D geovisual platform we present here, pilots, air traffic controllers, military officials, critical scholars of spatial control and militarized space, and others interested in an emergent vertical geopolitics can now see and explore the vertical dimension of US-controlled airspace. Previously invisible airspaces thus become observable, making subsequent questioning, analysis, and interpretation more feasible. For instance, from the geovisualizations we have generated, it becomes readily apparent that certain patterns of controlled airspace exist, especially as one moves exterior to the continental United States (the interior of the US is also replete with controlled “Class” airspaces, which makes perfect sense considering the FAA’s mission of providing a safe, efficient aerospace system). The vertical boundaries of controlled and Special Use airspaces effectively surround the main territory of the continental US, Hawaii, and Alaska, which perhaps comes as no surprise, but also surround other territorial interests such as Cuba and island nations across the Pacific. In these examples, critiques about the global reach of US spatial authority take on new and more vivid meaning by virtue of the 3D visualizations that render them legible.

For military officials, air traffic controllers, or others primarily concerned about ensuring airspace safety, the security of the US’s vertical territory, and national interests, our 3D interface can also highlight potential gaps or lapses in the vast network of controlled airspaces (though as Figure 13 illustrates, the protective curtain of the US area defense identification zone, at least, appears to be quite comprehensive). While our intent with this initial 3D visual platform is not necessarily to deliver a tool that can be directly taken up by pilots or air traffic controllers, by providing a proof-of-concept and presenting a methodology and example of how these complex three- and four-dimensional spaces can be made visible, we anticipate subsequent work could be applicable to improve transportation safety, as well as more fully realized understandings of vertical geopolitics.

We recognize certain limitations to what we provide here. In some cases, it is difficult to interpret why airspace classifications exist as they do. Some Prohibited Areas, for example, respond to obvious national security interests such as the airspaces above the US Capitol Building and the White House, but others are less intuitive. An extensive restriction in place above the Boundary Waters Canoe Area Wilderness in northern Minnesota is not due to national security concerns, as far as we can tell, but from a 1949 Executive Order (10092) to protect wilderness values above this remote region of lakes and forest (3 CFR 1949 Supp.). There are other controlled and Special Use airspaces that are difficult for us to explain, such as Class A airspaces applied to the Kamchatka Peninsula in Russia, and much of Papua New Guinea (these are likely simply an effort to coordinate remote jurisdictions in the interest of aerospace safety). Some SUAs appear to serve effectively as blank spaces on the map where flights are restricted or prohibited but the reasons for this are not readily accessible. Some of these “blank spaces” may be intentional in support of national security interests, while others are not in any way clandestine but the explanations for them may simply be buried in aeronautical guides not easily found by laypeople.

Casting toward future developments that could come from the platform and analysis we provide here, we envision a participatory GIS component (PGIS) integrated into our 3D visual platform. The platform is currently limited in that it functions as a one-way communication platform. To enhance its capabilities, we envision transforming it into a knowledge collection system. Although the platform includes various interactive features to facilitate information discovery, users are unable to input information, preventing it from becoming a two-way communication system. Allowing interested individuals and parties to contribute content through comments would enrich the information related to airspace historical data and characteristics. This could allow users to pose questions—Why is this airspace restriction applied here?—that could be engaged by other users and over time build greater public understanding of specific airspace objects and broader patterns of regulated airspace. There could also be opportunities in a PGIS environment to connect the research we provide here on US airspaces to international airspaces.

The global airspace ecosystem is becoming ever-more complex [64]—and in many places, more hazardous—and engaging with the tool we provide here to connect with other airspace domains could contribute to aerospace safety and knowledge more broadly. Our visualization platform can be further improved to address its current limitations. The US Federal Aviation Administration (FAA) regularly publishes updates to reflect changes in US airspace boundaries and restrictions. In this paper, we have focused on visualizing airspace data from a specific time period, from 17 June 2021 to 2 August 2021. However, the platform can be enhanced to visualize data outside of this timeframe by incorporating historically published FAA data and integrating newly published data in real time. This enhancement would upgrade the platform’s ability to handle complex four-dimensional geographic data, encompassing horizontal, vertical, and temporal dimensions.

In this paper, we have analyzed and displayed the complex, far-reaching, and many-layered geographies of US-controlled airspaces. These airspaces, which include Class, Special Use, and other categories, circumscribe North America and reach across the Pacific and Artic Oceans and into strategic portions of the Caribbean. Our work for the first time provides an estimate of the total volume of this controlled airspace. While invisible to view and rarely noticed outside of aviation professionals, controlled airspaces play an important role both in maintaining aerospace safety and asserting a vertical dimension of spatial authority by the US. In addition to calculating and portraying the extent and character of controlled airspaces, we also have described some of the key challenges faced when pursuing this work. The interactive, accessible 3D visual platform we have developed and present here will be a useful catalyst for further research into the diverse implications of controlled airspaces, where these exist, and how they function.