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Exercise 3: Change detection (cont'd) 
The following exercise will be performed by manual image interpretation. Observe the differences between urban and rural areas (vegetated area and bare soil). You will notice that urban areas are much more 'speckled', i.e. they appear as much less homogeneous surfaces. Indeed the pixel values vary a lot from pixel to pixel. This is because there is a dense mixture of houses, small gardens and streets. The eye is able to distinguish between these, but the computer less so! A good way to learn how to distinguish different land cover is to compare the details of your image with the image ‘Cordoba, Argentina’ provided by Google Earth. Since our images are geocoded, you will be able to find the corresponding location (Latitude, Longitude) with high precision. Now you can map the urban areas in the 1992 and 2009 data using the GIS tool. In order to guide you, we have done it for the 1972 data. The file is called city_boundary_1972.shp. Open the 1992_cordoba bands 453 and contrast stretch it to get the urban areas well contrasted. Open City_boundary_1972.shp For the Transformation Method (if requested: UTM - WGS84, zone 20, Hemisphere S.) For LEOWorks 3: Open the GIS tool and the City_boundary_1972.shp For the Transformation Method use 'Arbitrary' and 'Map Based'. Look at the city boundaries from 1972 displayed on the 1992_Cordoba image. Now create a new theme and name it 'urban_1992'. Digitise the urban boundaries in the displayed 1992_Cordoba false colour image. You will see that there have been a lot of changes between 1972 and 1992. Save the urban_1992 boundary file. Do the same with the 2009_cordoba bands 453 image. Display and use the interactive stretching to enhance the image if necessary. Open the 'urban_1992' boundaries file and observe the city boundaries of 1992 now visible in the 2009 image. Open a new theme, call the file 'urban_2009', and digitise the 2009 urban boundaries. To get a good overview of the urban development of Córdoba do the following: Open the 1972_cordoba image using bands 4, 3 and 2 to create the RGB (red green blue) image and strongly enhance the contrast. On this image, open all three GIS-layers (urban_1972, urban_1992 and urban_2009). Make use of the GIS Tool by giving each boundary a different colour without fillings of the polygons (Edit, Properties, Layer Editor). Have a look at the procedure used to estimate the area of polygons in the LEOWorks Tutorial.
For LEOWorks 3: You can use the GIS>Tool>Information to get the accurate surfaces of each of the polygons. Remember that you have to multiply the number of the pixels in an area of 60m x 60m.
3. Discuss the two different methods you have learned and the results achieved. Which one is the most reliable? Be aware that what you have just undertaken using GIS is a very common procedure used by professionals!
4. Produce a report with your results and present it to people who are interested in politics and urban development.
A similar exercise can be done on any city or rural area of the world – even your own! For free worldwide data from Landsat and other sensors we suggest you connect to the USGS Global Visualization Viewer or to the free Global Orthorectified Landsat Data.
Last update: 23 October 2013
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