*3.1. Land Use Maps, Land Use Changes, and Validation Results*

The produced 30 m resolution land use maps of Hanoi for the years 2016 and 2017 are displayed in Figure 4a,b, respectively. Some areas with substantial land use changes are visually chosen and labeled as A, B, C, E, and F in Figure 4c,d, with coverage percentage statistics for the three major types of land use of concern in the years 2016 and 2017, respectively. The three major land-use types include built-up areas, vegetation covers, and water bodies. It is found that the changes in land-use coverage percentage are 4.4%, −4.4%, −0.8%, and 0.8% for built-up, vegetation, water, and others, respectively, from years 2016 to 2017. The 4.4 % area of inner Hanoi City is equivalent to 704 ha (7.04 km2). Obviously, the increase in built-up area is mainly contributed by the decrease in vegetation coverage by 4.4%. However, it does not mean that built-up area is completely transformed from vegetation cover, since there are other minor land use covers. Even though we only consider the land-use changes in a one year interval from 2016 to 2017, the fast change of land use in inner Hanoi City is obvious by comparing the two consecutive years of images.

After the quantified areas of land use changes, qualitative land use changes may be easily observed by comparing the Google Earth images, which are conveniently available online, as well as field survey photos, as shown in Figure 5. Field survey photos were taken on 14 October 2018. The transformation of vegetation cover into built-up areas is easily detected by bare eyes. Figure 5a shows Google Earth image of Inner Hanoi City with areas B and E for the demonstration of land use changes and (red) dots with field survey photos as the ground truth for reference. Figure 5b,c are Google Earth images of area B that were acquired in June 2016 and August 2017, respectively, with four field survey photos showing the current in-situ land use status. Figure 5d,e are Google Earth images of area E, acquired in June 2016 and August 2017, respectively, with two field survey photos confirming the current in situ land use status of either built-up or ongoing construction circumstances.

**Figure 4.** Land-use maps of inner Hanoi city for (**a**) 1 June 2016, and (**b**) 4 June 2017. Areas with substantial land-use changes are visually chosen and labeled as A, B, C, E, and F in (**c**) and (**d**) with coverage percentage statistics for the three major land-use types of concern and others in the years 2016 and 2017, respectively.

The accuracy assessment of LULC classification was performed to quantitatively assess how effective the pixels were sampled into the correct LULC classes. The accuracy assessment of pixel selection was on areas that could be clearly identified on both Landsat high-resolution images, and on Google Earth and Google Map. A total of 300 points (locations) for both years 2016 and 2017 were created in classification images of the study area, as presented in Section 2.4. The study had an overall classification accuracy of 92%, a kappa coefficient (K) of 0.88, an overall accuracy of 93%, and kappa coefficient (K) of 0.9, 0 for 2016 and 2017, respectively. The confusion matrices of LULC classification maps derived from Landsat 8 images in 2016 and 2017 are shown in Tables 3 and 4, respectively. The kappa coefficient is rated as being substantial, and hence, the classified image was found to be appropriate for further analysis.

**Figure 5.** Field survey photos taken on 14 October 2018 are overlaid onto Google Earth images. (**a**) Google Earth image of Inner Hanoi City with areas B and E for the demonstration of land use changes and (red) dots with field survey photos as the ground truth for reference; (**b**,**c**) are Google Earth images of area B acquired in June 2016 and August 2017, respectively, with four field survey photos confirming the current built-up status; (**d**,**e**) are Google Earth images of area E acquired in June 2016 and August 2017, respectively, with two field survey photos confirming the current built-up status and on-going construction circumstances.


**Table 3.** Confusion matrix of land-use map classified from the Landsat 8 image in 2016.


**Table 4.** Confusion matrix of land-use map classified from the Landsat 8 image in 2017.

Table 5 shows the land-use classification and its changes from years 2016 to 2017 in inner Hanoi City. It reveals a big increase for built-up areas by 8.9% in a year, but a decrease for vegetation, water, and others by 10.9%, 7.0%, and 4.0%, respectively. For assessing the quantity of transformations among land-use types from the years 2016 to 2017, a transformation matrix is determined, as shown in Table 6. Two key points are observed from the table. First, increased built-up area 841 ha is primarily changed from vegetation (618 ha), followed by others (137 ha) and water (86 ha). Second, the transformations of built-up to vegetation, water, and others are 0.33% (27/7937), 0.27% (22/7937), and 0.92% (74/7937), respectively.

**Table 5.** Land-use changes between years 2016 and 2017 in inner Hanoi.



It is evident that, under the Master Plan 2030, the inner Hanoi City has been changing quickly with time, since the implementation of the Plan in 2011. This can be easily justified by the dramatic land cover changes in a year, by comparing the land-use maps of years 2016 and 2017. Under such a fast-changing land-use situation, any suggested measures for mitigation of UHI for the inner Hanoi City are urgently required.
