Analyses And Discussion
In our study, we assumed that there is an operational GIS that stores an old city map and multi-temporal RS data sets. To acquire primary digital data stored within the GIS the selected classes: a ger area (a Mongolian national house) and building parcels were digitized in a UTM map projection from a topographic map of the test area, scale 1:25.000. There have been selected only two classes because on the satellite images it was not possible to distinguish between land parcels related to apartments, residential houses and industrial buildings. The digitized city map is shown in figure2. To define the total area of each class the vector map was rasterized with a pixel size of 10m and then a number of pixels falling into each of the classes has been calculated. The result indicated that in 1969, ger area covered 624ha whereas building parcels occupied 1566ha. Although, we have census data of Ulaanbaatar, it is not possible to directly relate it to our analysis because due to a lack of data, our study area covers more central and western parts and a part of eastern block of the capital city. Therefore, census data has been used to see just general increase of population at different years. As it was seen from the census data, in 1969 the city had 267.400 inhabitants.
Figure 2. A digitized city map of Ulaanbaatar
As it has been mentioned before, the aim of the study is to compare the changes occurred in central part of the city during the centralized economy with the changes occurred during the market economy. For this purpose, SPOT PAN data of 1990 and SPOT XS image of 1997 could be compared with the digital GIS data. However, for the interpretation it is better to use a colour image if it is available. Therefore, to have more spectral variation of the selected classes, SPOT PAN data was integrated with SPOT XS image of 1986. The processing of the images has been carried out as follows [1,2]:
Initially, all the images were thoroughly analyzed in terms of distortion and brightness. The images were of a good quality but only the panchromatic data had to be radiometrically corrected. Radiometric correction of panchromatic data was done by averaging upper and lower lines of the stripes that had to be corrected. Then, SPOT images of 1986, 1990 and 1997 were successively geometrically corrected to the UTM map projection using the same topographic map of the study area. The ground control points were selected on well defined cross sections of linear features. For the actual transformation, a second order transformation and nearest neighbour resampling approach have been applied and the related RMSs were 0.38, 0.47, 0.58, respectively. Further, from each image the same set of subsets falling into the same image frame has been chosen. To create an integrated colour image the multispectral image was firstly sum normalized in order to eliminate different influences and then multiplied by the intensity of the panchromatic data. After this, the normalized bands have been assigned to RGB colours accordingly (figure3).
It can be expressed by the formula:
R=(NIR/NIR+R+G)*PAN
G=(R/NIR+R+G)*PAN
B=(G/NIR+R+G)*PAN
where NIR,R,G - bands of SPOT-XS, and PAN - panchromatic band.
Figure 3. The integrated image of Ulaanbaatar (SPOT XS-86 + SPOT PAN-90)
To create a city map of 1990, on the enhanced image the selected classes were screen digitized and then rasterised with a pixel size of 10m. Moreover, the statistics of each class was calculated. The result indicated that the ger area and building parcels covered 1236ha and 1987ha, respectively, while population of the city had become 574.900. As seen, within a 21 year period, ger area increased by 98% and building parcels increased by 27%, while population had increased by more than 2 times. It has the following reasons:
- during the centralized economy, due to the industrialization process in the city many people came from rural sites with their gers to the city;
- gers are surrounded by fences covering usually 600-800sq.m, thus covering large area;
- during the socialist economy as residential houses mostly building blocks with many floors and flats were built. Although, a few residential blocks could contain families of a whole ger district, they occupy much smaller land parcels than gers' parcels.
A map indicating the changes occurred in Ulaanbaatar area during the centralized economy is shown in figure 4.
Figure 4. A map indicating the changes occurred in Ulaanbaatar area
in between 1969 and 1990
