Land Cover and Land Use Ontology—Evolution of International Standards, Challenges, and Opportunities

Abstract

Knowledge of land is of central importance to manage the impact of mankind upon the environment. The understanding and treatment of land vary greatly across different regions and communities, making the description of land highly specific to each locality. To address the larger global issues, such as world food production or climate change mitigation, one needs to have a common standardized understanding of the biosphere cover and use of land. Different governments and institutions established national systems to describe thematic content of land within their jurisdictions. These systems are all valid and tuned to address various national needs. However, their integration at regional or global levels is lacking. Integrating data from widely divergent sources to create world datasets not only requires standards, but also an approach to integrate national and regional land cover classification systems. The ISO 19144 series, developed through the collaboration between the Food and Agriculture Organization of the United Nations (FAO) and the International Organization for Standardization (ISO), offers a meta-language for the integration of disparate land classification systems, enhancing interoperability, data sharing, and national to global data integration and comparison. This paper provides an overview of classification system concepts, different stages for the development of standards in ISO and the status of different standards in the ISO 19144 series. It also explores the critical role of the ISO 19144 series in standardizing land cover and land use classification systems. Drawing on practical case studies, the paper underscores the series’ potential to support global sustainable development goals and lays out a path for its future development and application. Using these standards, we gain not only a tool for harmonizing land classification, but also a critical level for advancing sustainable development and environmental stewardship worldwide.

1. Introduction

In a world grappling with climate change, land degradation, desertification, biodiversity loss, and the need for sustainable development, understanding and managing mankind’s impact on the land is more important than ever [1]. Land cover and land use information proved to be the key information and data layer in the United Nations [2], as well as in natural resource monitoring [3], land use planning [4], agricultural planning and monitoring [5], and disaster risk management and assessment [6,7], and is critical not only for achieving sustainable development goals (SDGs) [8,9], but also for international and national reporting frameworks. Early efforts were largely fragmented, with individual countries and regions developing their own classification 1 systems for defining land cover and land use classes tailored to local conditions and priorities [10,11,12]. While these efforts significantly improve land cover and land use mapping, they simultaneously introduce challenges related to data integration and comparison at a regional and global level. Differences in land cover ontologies, definitions, and related difficulties in creating one-to-one relationships between the two systems often limit the utility and comparability of land cover maps across time, space, and organizations. Therefore, standardized frameworks are needed to overcome these growing issues. This paper introduces a global standardization framework designed to address the previously mentioned gaps in the field. Furthermore, this framework incorporates the potential for definition conversion and translation from various existing systems by making it dynamic through the use of a meta-language. A metalanguage is a language used to describe, analyze, or define another language. It is a higher-level language that provides the vocabulary, grammar, and rules to discuss and structure the properties and elements of a primary language [13].

Standards are the invisible glue that enables society to manage sustainably natural resources and develop infrastructures. They provide a framework that allows different elements within society to interwork [14]. They are also needed in achieving SDGs by providing framework and guidelines that ensure consistency, safety, quality, and interoperability across various sectors. Standards enable governments, stakeholders, and communities to achieve the SDGs through well-defined, measurable, and replicable practices. Standards for geographic information began over 450 years ago with the work of Gerardus Mercator and his contemporaries, who established a firm mathematical basis for cartography. Together with Abraham Ortelius, Mercator established a relatively accurate atlas of the world called the Theatrum Orbis Terrarum [15]. This was the beginning of a rapid advancement in geographic knowledge based on the “standardization” of cartographic principles. The ISO Technical Committee 211 on Geographic Information/Geomatics establishes a structured set of standards for information concerning objects or phenomena that are directly or indirectly associated with a location relative to the Earth. These standards specify methods, tools, and services for data management, including acquiring, processing, analyzing, accessing, presenting, and publishing data for users and systems 2 [16]. ISO/TC 211 Working Group 7 on “Information Communities” focuses on standardization issues related to conceptual modeling of geographic features, including many aspects of land, such as land cover, land use (in the ISO 19144 series of standards), and Land Administration (in the ISO 19152 series). ISO/TC 211 Advisory Group 13 on “Land Cover and Land Use” advises ISO/TC 211 on the implementation of land cover and land use standards in the UN and other transnational organization 3.

The ISO 19144 series, by FAO and ISO, represents a pivotal advancement in this endeavor, offering a harmonized framework for the classification of land cover and land use that transcends national boundaries and varying local definitions [17,18]. This series provides a metalanguage for integrating diverse land classification systems and address land characterization allowing for the description and comparison of various land cover or land use legends or application schema.

As we move forward, the role of standardized land classification becomes increasingly integral to achieving the United Nations Sustainable Development Goals (SDGs). The ISO 19144 series not only enhances our ability to monitor and manage the land effectively, but also serves as a foundation for collaboration and innovation in environmental stewardship. This introduction section provides a general overview of the importance of harmonized land cover and land use ontology and the basic introduction of the ISO 19144 series. The second section explains the concept of classification system standards, its process, and standards in the ISO 19144 series. Section 3 discusses the case studies, applications of the ISO 19144 series, their status, and synergies with other ISO standards. Section 4 provides the conclusion and future aspect.

2. Classification System Standards

2.1. The Concept

The world in which we live is very complex. A description of land must include both the physical nature of the surface of the earth as well as a representation of the uses that mankind applies to the earth. This can be infinitely complicated, including the biophysical aspects covering the surface of the earth, the abiotic surface elements of the earth, as well as the functions and activities that relate to the use of land. Different aspects of the environment may be applicable in various situations. The amount of forest cover or other green carbon dioxide-absorbing flora may be of importance in calculating greenhouse gas emission. Other parameters are important in measuring and predicting food production. The number of parameters involved in understanding all aspects of land cover or land use are enormous. The classical approach to addressing this complexity was to establish a classification system. A “legend” or application schema was developed that includes the relevant categories that need to be measured, and raw data extracted from satellite imagery, ground surveys, or other sources are ascribed to the various categories [13].

There were many classifications system and legends developed over time by different nations or organizations to suit their own needs. Some of these are general, such as the European Environmental Agency CORINE system [19], or the US Geological Survey Anderson Legend [20]. In Europe, the original CORINE system was made into a much more flexible application schema by the EAGLE group [21,22]. To address the wide diversity of land cover systems in Africa [13,23], and in developing nations, and to link to those systems in developed nations, FAO developed the land cover reference system in West Africa [24]. This system was also not just a simple legend but a flexible application schema that could be structured to address many different application areas.

In 2004, the FAO and ISO/TC 211 established a cooperative agreement to jointly develop international standards to address the harmonization of land classification systems [25]. As a result, the ISO/TC 211 19144 series was developed. In 2009, the standard ISO 19144-1 Geographic information—Classification systems—Part 1: Classification system structure was published [18], and in 2012, the standard ISO 19144-2 Classification systems—Part 2: Land Cover Meta Language (LCML) was published [17]. The first part of the standard gives a high-level framework for classification systems and describes how registration may be used to extend the meta language to encompass any classification system. The second part of the standard, i.e., LCML, operates by describing each land cover class in a classification system in terms of a set of basic elements with associated attributes expressed as properties and characteristics. A whole land cover (or land use) classification system can be modeled by combining these basic elements. The basic elements in the meta language provide a system-independent vocabulary with which to describe a land cover (or land use) class [17]. These standards do not provide a standardized legend or name of classes, but provide a standardized, systematic, and parametric approach to create or define land cover or land use classes or legend.

The basic elements in the meta language for describing land cover are based on a purely physiognomic description of reality. These elements may be organized into strata (or layers) so that classification classes may represent complex structures. A classic example of layering is the canopy effect of the trees over a grass layer. The elements may also be organized horizontally to represent horizontal patterns. A land cover class to be described may consist of two or more sub elements having a specific horizontal arrangement. An example illustrated in the standard is a “tiger bush”, which is a specific type of vegetation formation consisting of the combination of dense shrubs and open grassland in a distinct pattern. It occurs on low slopes in arid and semi-arid regions in areas such as Australia and West Africa. A horizontal pattern may be defined to describe the pattern cover percentage of each of the basic elements in the pattern [17,26].

Moreover, two different land cover classes (from different land cover classification systems) can be compared by examining the elements of which it is composed. If one classification class from one system is composed of element A + element B + element Y + element Q, and another of elements element A + element B + element Y, then it can be determined that the difference is the Q element. Being able to compare land cover classification systems in this detailed manner is important for establishing mappings so that data sets can be generated by the fusion of data from different sources [17,26]. The meta language establishes a vocabulary which can be used to describe a land cover class from any classification system. This vocabulary is established on a decomposition based on the physiognomic aspects of each element. This is partially illustrated in Figure 1. This vocabulary is not a classification system, but rather is an ontology which can be used to describe a class in a land cover classification system.

In addition to the basic elements, one can add properties and class characteristics to further refine the description of any land cover class. The example in Figure 2a shows a tree and shrub savannah, which may be a class in a particular classification system. A savannah is composed of three separate layers of trees, shrubs, and herbs with different covers of the woody component types. The base layer is composed of herbs. The second and third layers are composed of shrubs and trees of different heights and cover, as can be seen in Figure 2a. By adding details on properties and characteristics, this class can be modeled in LCML, as shown in Figure 2b.

Land use is a separate description of land that describes the economic or other functions or other purposes that humans apply to land and the activities performed on the land associated with these functions [27]. A description of land use in a particular country or region may be linked to national and regional customs, legislation, or economic factors, and there may be quite a variation between the way land use is expressed. The administrative and economic purposes for gathering land use data may vary widely. However, land use is an important complement to a land cover description. This means that the use of a meta language to describe land use is even more important. Because the purpose of land use varies even more than land cover, it is difficult to establish a detailed ontology. Many of the details need to be defined using a registration process that allows for an evolution of the standard. That is, users of the standard may register detailed code list entries and other attribute types and values to a common register that may grow with use. The land use component of the schema is based on a functional interaction between “Functions” and “Activities” [28]. Functions refer to the specific purposes that a particular piece of land serves and the specific output it provides, whereas activities refer to what actually takes place in physical and/or observable terms on the land defined under a specific function.

Functions can be defined by the sequence of specific actions on a given type of land cover. The main five functions are (1) production: the process of growing, harvesting, or making goods; it refers both to the growing of plants or animals and the process and methods used to transform tangible raw materials into goods. (2) Provision: the action/process of providing or supplying of intangible products for other business or consumers; it refers to the provision of services, utilities, transport, or logistic. (3) Residential: the action/state of providing housing, including both single and multifamily houses when not linked to direct and secondary production. (4) Regulative: the action/process/state of managing through specific normative rules (controlling, directing, monitoring, or managing). Detailed rights, restrictions and responsibilities, and parties associated with a “regulative” function may be described in accordance with the Land Administrative Domain Model specified in the ISO 19152 series of standards, and (5) other: undetermined or insubstantial use. A list of activities is defined for each of the main functions [28].

2.2. Land Characterization

Both land cover and land use are often used together to “characterize” land [28]. The proposed ISO land cover and land use standards are designed to be linked. There are five basic combinations defined, including (1) pure land cover: addressing only the physiognomic aspect of land. (2) Augmented land cover: with some land use functional elements (this is a common case). (3) Pure land use: addressing only functions and activities. (4) Augmented land use: with some land cover class characteristics, and (5) full land characterization: including both land cover elements and functions and activities on land.

2.3. ISO Process and an Approach to Standardization

ISO is an international consensus standards organization based on memorandums of understanding between nations. Almost all nations on earth are members. The ISO process is slow and labor intensive, but it is designed to develop consensus, and it is very successful at creating such consensus. A standard in ISO goes through several stages, and details are provided in

Table 1. Different stages of standard development process in ISO.

Stages	Description
Proposal stage	An ISO member state or liaison organization submits a NWIP.
Preparatory stage	A project team develops a work draft document or a draft revision of an existing standard.
Committee stage	The entire committee ballots the document and an Editing Committee under the management of the ISO/TC 211 Working Group debates the proposed revisions and instructs the editor to revise the document. The proposed standard may go through several versions at this stage before agreement is established.
Enquiry stage	A ballot is issued to all participating and observing ISO member states for voting and liaison organizations for comment. Final comments are processed by the Editing Committee. In theory, all contentious issues should be resolved at this stage, but at times, some conflict may remain.
Approval stage	A final ballot, without comments, is taken to approve the standard.
Review stage	A periodic review takes place, typically every five years.

Source: ISO [29].

.

The ISO 19144-2 LCML went through all these stages and became standard in 2012. This joint standard between ISO and FAO and the document are the responsibility of both organizations under a cooperative agreement signed between the FAO and ISO/TC 211. When the standard came up for systematic review, it was decided to revise the standard and extend it to address land use.

The preparatory stage (stage 0) allows for initial work to be carried out to plan the standard development. A stage 0 review was conducted on the whole ISO 19144 series of classification standards to study the direction for revising ISO 19144-2, the creation of a set of registers of world-wide legends, and the introduction a New Work Item Proposal (NWIP) for the standardization of land use functionally linked with land cover.

2.4. A New Land Use Standard

Land use builds upon land cover, but it is a different topic. A new separate standard for land use (ISO 19144-3) was proposed that builds upon the ISO 19144-2 land cover standard [30]. The ISO 19144-3 standard will not only describe land use, but it will also describe the method of combining land cover and land use to produce land characterization [30]. Specifically, a second schema was developed for land use, defining land use functions and activities. The land use model ensures a fully functional inter-connection of the two components. In fact, they are not separate entities, but must be considered as a completely integrated system when used together to describe land.

3. Discussion

The potential of the work and contribution of the ISO series was highlighted and discussed using various case studies, applications, synergies with other ISO standards, and status of standards in the series.

3.1. Case Studies

The adoption of the ISO 19144 series across different regions and projects demonstrates its versatility and effectiveness in addressing global challenges related to land use and cover. The following case studies and available applications illustrate how these standards can facilitate interoperability, data sharing, and integration, contributing to sustainable development goals. By providing a standardized framework for land cover and land use classification, these standards can not only enhance interoperability and data sharing, but also support informed decision-making in agricultural optimization.

3.1.1. Case Study 1: Assessing Land Degradation in the South America

The application of the ISO 19144 series in assessing land degradation efforts in South America highlights its critical role in environmental conservation efforts. By standardizing land cover classifications, stakeholders, including government agencies, NGOs, and researchers, were able to integrate data from various satellite imaging sources, enhancing the accuracy of land degradation. For example, for Uruguay, a comparative assessment of land degradation using European Space Agency Climate Change Initiative Land Cover (ESA CCI LC) and national land cover data for 2000 to 2015 revealed distinct segregation in the national land cover transition matrix, particularly separating native forests from exotic species plantations, which are classified similarly to crops, highlighting their different soil degradation behaviors and significant impact on Uruguay’s land cover [31]. The SEPAL 15.3.1 module was used for this assessment (https://docs.sepal.io/ (accessed on 15 July 2024)).

3.1.2. Case Study 2: Agricultural Land Use Optimization in West Africa

In West Africa, the ISO 19144 series supported agricultural projects aimed at optimizing land use for food security. By standardizing classifications for agricultural land, the projects integrated local and national data, identifying underutilized or poorly utilized areas. This enabled targeted interventions to improve agricultural practices, enhance crop yields, and promote sustainable land management among smallholder farmers. For example, in The Gambia, a framework was developed for monitoring geospatial indicators of the Resilience of Organizations for Transformative Smallholder Agriculture project. Baseline information was developed using LCML and geospatial tools and platforms, and the data were used to monitor and assess progress in various sectors, including the rice sector, vegetables sector, mangroves sector, and forest sector [32].

3.1.3. Case Study 3: Development of Land Cover Reference Systems

At the regional and national level, various land cover reference systems were developed to support data harmonization, interoperability, and comparability. The importance and complexity of creating a regional or national land cover reference system is very often underestimated. The availability of international standards is an important step in the creation of a common syntax for the rationalization and harmonization of national and regional classification systems.

The land cover reference system is a systematic overview of the different land cover aspects of a region or area and is represented and ordered according to an “object oriented” logic using ISO standard, i.e., 19144-2. Following a specific procedure, a user can prepare his own land cover legends. Figure 3 presents an overview of land cover reference system components and their functional relationships. There are different levels in a reference system or a schema and in each level the land cover features are arranged in meta-groups. The built-up of each group and its position in the schema is regulated by specific rules. The user is free to navigate inside the schema selecting; for instance, a class of vegetation at the very detailed level of the system and another one of agriculture at a more general level. The user must remember that those are meta-classes that can later be further customized according to specific needs.

West African Land Cover Reference System

The critical need to deliver timely and consistent information on global land resources is underscored by the detrimental effects of land degradation on food production, environmental quality, living conditions, and health, particularly in West Africa, where declining yields and increasing poverty highlight the importance of regional collaboration for sustainable development. Additionally, the use of outdated or different classification systems in countries and within countries and the lack of a common, harmonized framework result in inconsistent land cover information, making data integration more difficult at not only the national but regional level. Efforts were made to enhance capacity in the region, leading to the successful creation of the West Africa Land Cover Reference System (WALCRS). The WALCRS is the first harmonized land cover reference system developed for West Africa in collaboration with international and regional institutions [24]. The system attempts to instantiate all these basic requirements in an innovative logical framework adapted and refined for West African countries. It is based on three basic levels, starting from the more general classes to the more detailed classes. The Gambia is the first country that implemented this regional land cover reference system to support small holder agriculture in the country (case study 1). Efforts are currently underway to implement this system in other parts of the region.

Tunisia Land Cover Reference System

The national land cover reference system of Tunisia, based on the ISO 19144-2 standard, follows the arrangement rules and meets the needs to represent all types of land cover features across the country [33]. This reference system is developed to enhance the national land cover map for the national forest inventory as well as thematic maps under national sustainable development programs, natural resource management, land degradation assessment, and climate change effects monitoring. Moreover, this framework will allow diverse users to incorporate additional meta-classes and extract the deferred legend. Recently, a land cover map was prepared for the country to promote resilient agriculture, combat land degradation, and adapt to the impacts of climate change. The main objective of this study was to analyze crucial crops, understand their specific requirements, and acquire geographic and statistical information related to these crops [34].

3.2. An International Library Based on ISO Standards: Land Cover Legend Registry (LCLR)

Consistent land cover ontologies at the national level are crucial for ensuring data standardization and comparability, which support effective policy implementation and natural resource monitoring. To ensure the consistency and availability of interoperable land cover legends, FAO developed an online registry. The land cover legend registry (LCLR) stands out as the first international platform, providing exhaustive information on land cover legends at the sub-national, national, and global level, and supporting multiple languages and formats [35]. This registry serves as a centralized repository for land cover classifications. It ensures that land cover data are consistently categorized and easily accessible worldwide, adhering to internationally recognized standards [36]. By standardizing land cover legends, the LCLR facilitates seamless data exchange, comparison, and integration across different regions and platforms. This enhances global collaboration in environmental monitoring, research, and policymaking, enabling more informed and coordinated efforts in land use planning, conservation, and sustainable development. This registry can support the forthcoming ISO standard on registries and serve as a foundation for future global registries.

3.3. A Tool Based on ISO Standards: Land Characterization System Software (LCHS)

Inconsistent land cover legends hinder their effectiveness, especially with advancements in remote sensing technology. Ontologies improve the standardization and harmonization of land cover taxonomies, reducing inconsistencies and leveraging computing power for better, faster scientific answers. Yet, without suitable tools, using ontologies can be challenging. An innovative tool, the land characterization system (LCHS), was developed by FAO in collaboration with the Italian National Research Council (CNR). It supports the ISO 19144-2 and is designed to streamline and accelerate the creation and editing of land cover legends through a data-driven approach [37]. The tool is open source and can be accessible online (https://lchs.fao.org/ (accessed on 15 July 2024)). Anyone can define their land cover classes based on a common vocabulary and harmonized framework that can contribute to the global data harmonization.

3.4. Status of ISO 19144 Series

The work on the revision of the ISO 19144 series of classification standards has been ongoing for a number of years. The work began in June 2018 with the establishment of a stage 0 preliminary work item to review the ISO 19144 series of classification standards. A report was submitted in December 2019 [38] that recommended the development of a series of standards to address land cover and land use. The existing ISO 19144-2 land cover meta language standard was proposed to be revised to address only pure land cover, removing any land use components and any registration components. A new ISO 19144-3 technical specification standard on land use was proposed to address land use and the link between land cover and land use. A new ISO 19144-4 standard 4 on the registration of land cover and land use elements and of entire systems was proposed.

When the work on these three standards was completed, the existing ISO 19144-1 and ISO 19144-2 classifications systems, the overview and fundamentals standard, were proposed to be revised.

The current status as of July 2024 is that (1) the revision of ISO 19144-2 on land cover was published (12 December 2023). (2) The new ISO 19144-3 on land use passed its Draft Technical Specification ballot with 100% approval and is now in the publication stage. Some minor typographical and non-substantive technical errors identified in the DTS ballot will be addressed and the document should be published soon. (3) A new preliminary project on ISO 19144-4 on registration and implementation aspects was approved by resolution at the May 2023 plenary of ISO/TC 211 and a new work item proposal was submitted and is under ballot, and (4) work on the revision of ISO 19144-1 classification systems structure will not begin until the work on ISO 19144-4 is mature.

3.5. Synergies with Other ISO Standards: Enhancing Sustainability and Environmental Stewardship

The ISO 19144 series plays a pivotal role in land cover and land use classification, but its impact can be significantly amplified when used in conjunction with other ISO standards. Together, they can form a comprehensive framework for environmental management, biodiversity conservation, and climate change mitigation and adaptation. Understanding these synergies offers a holistic approach to sustainability and environmental stewardship.

3.5.1. Integration with ISO 14000 Series (Environmental Management)

The ISO 14000 family focuses on various aspects of environmental management, offering tools for organizations to minimize their environmental footprint [39]. When combined with the land classification insights from the ISO 19144 series, organizations can more effectively assess and manage their impact on land use and cover, leading to better conservation practices and reduced environmental degradation. The main purpose of linkage is (1) enhance environmental impact assessments, (2) support sustainable land management and conservation practices, and (3) inform environmental policy and planning at organizational and governmental levels.

3.5.2. Complementing ISO 37101 (Sustainable Development in Communities)

ISO 37101 provides a management system for sustainable development in communities, aiming to promote holistic and integrated approaches [40]. The land classification standards of the ISO 19144 series enrich this management system by offering detailed data on land use and cover, critical for urban planning, green space management, and infrastructure development in a sustainable manner. The main purpose of the linkage is (1) facilitate informed urban and rural planning decisions, (2) promote the conservation and sustainable use of green spaces and natural resources, and (3) support the integration of environmental considerations into community development projects.

3.5.3. Enhancing ISO 14064 Series (Greenhouse Gas Accounting and Verification)

The ISO 14064 series provides international standards for quantifying, monitoring, reporting, and verifying greenhouse gas (GHG) emissions [41]. The standardized land cover and use data from the ISO 19144 series are essential for accurately assessing the carbon sequestration potential of different land types, contributing to more reliable GHG inventories and informing climate change mitigation strategies. The main purposes of the linkage are to (1) improve accuracy of GHG inventories by incorporating land use data, (2) support the development and monitoring of carbon sequestration projects, and (3) enhance transparency and credibility in reporting GHG emissions and reductions.

By leveraging the synergies among these standards, organizations and governments can enhance their efforts in sustainability and environmental stewardship, leading to more effective and coordinated actions for preserving the natural environment and in facing global issues.

4. Conclusions

The implications of adopting and implementing the ISO 19144 series extend far beyond the technical realm of standardization. For policymakers, these standards offer a reliable basis for crafting evidence-based environmental legislation and land management policies that are harmonized across borders. For researchers, the series presents a unified language for exploring and communicating complex land cover and use dynamics, fostering cross-disciplinary collaboration and innovation and can contributes to interoperable and comparable data at local, national, and global levels. Using LCLR, researchers and stakeholders can now have access to interoperable data and legend information, thus can also prepare their own land cover and land use information using LCHS software (version 1 (prototype) and version 2) for consistent land cover information.

Looking ahead, several areas warrant further exploration to maximize the utility of the ISO 19144 series. First, expanding the scope of the standards to encompass emerging land use practices and novel ecosystems can ensure their relevance in a rapidly changing world. Additionally, increasing the accessibility and usability of these standards, particularly for low-resource settings, is crucial for achieving widespread adoption and impact. Future research should also focus on the integration of ISO 19144 series data with cutting-edge technologies such as artificial intelligence and machine learning, unlocking new possibilities for predictive modeling and scenario analysis in land use planning and environmental monitoring.

It is thus expected that the utilization and development of land cover reference systems and land cover and land use information based on the ISO 19144 series will help to reduce inconsistency issues in information and support the data comparability, integration, and translation, thus improving the quality, robustness, completeness, and transparency of the information. The journey toward a more sustainable and equitable use of our land begins with a shared commitment to standardization and collaboration, as embodied in the ISO 19144 series.