Web Mapping Illustrated

Preprocessing Data Examples

Projects in this chapter focus on the city of Kelowna, Canada. In the summer of 2003, there were massive fires in the area. It was a very destructive fire season, destroying many homes. This area is used as a case study throughout the rest of this chapter as you work through a personal mapping project in the area. Many of the typical problems, like trying to find good base map data, are discussed.

In order to use base map data, you need to do some data preprocessing. This often involves clipping out areas of interest or projecting information into a common coordinate system.

Clipping Out an Area of Interest

The satellite image used for this project covered a much broader area than was needed. Unnecessary portions of the image were clipped off, speeding up loading and making the image a more manageable size.

Tip

Satellite imagery of Canada is readily available from the government's GeoGratis data site (http://geogratis.cgdi.gc.ca/). The scene for Kelowna is path 45 and row 25; you can grab the image file from the Landsat 7 download directory (/download/landsat_7/ortho/geotiff/utm/045025/). The files are organized and named based on the path, row, date, projection, and the band of data in the file. The file ...743_utm10.tif contains a preprocessed color composite using bands 7, 4, and 3 to represent red, green, and blue colors in the image.

I used OpenEV to view the file and determine the area of interest. Figure 9-1 shows the whole image or scene.

The large lake ...