Creating a Map

Have you ever wanted to create a map? Now you can! Professional grade geographic information system or GIS software can be downloaded free of charge from the wonderful people at QGIS.org for Mac, Windows and other platforms. Standard data layers such as roads, buildings and water bodies are available free at openstreetmap.org.

Digital elevation model (DEM) data is available to the public at EarthExplorer.usgs.gov. This now includes space shuttle radar topography mission (SRTM) data at 1 arc-second resolution. DEMs divide up an area into tiny squares and assign an elevation value to each square. Smaller squares provide more detail. With the SRTM 1 arc-second data, the squares are roughly 30 meters by 30 meters. This is good enough for most water supply system analysis and design tasks.

For very large areas, this level of detail is too much. The image above shows global multi-resolution terrain elevation data (GMTED) which is available at resolutions of 7.5, 15 and 30 arc-seconds. You can load different resolutions for the same location into the QGIS and configure it to swap between them as you zoom in or out.

To create the image above I set up a colour ramp. Everything at elevation zero or below is blue, everything between 0 and 20 meters is yellow etc.

If you wish to add spot locations such as cities, you can do this in Google Earth, save as .kml and import into QGIS. On the image above you may be able to spot Istanbul.

A word of warning: the image above is of course distorted. It shows the curved surface of the earth as flat. It appears to indicate that the distance along the top of the map is the same as the distance along the bottom, but this is not true. For measuring distances you will need to assign an appropriate geographic projection or use Google Earth.