Finding Potential Sites for Small-Scale Hydro Power in Uganda: a ...

3 Theoretical Background and Rural Development3.1 GISThe definition of GIS according to Ekundh (1999) is:“A computerized information system to handle and analyze geographical data.”GIS stands for Geographical Information Systems and is simply a combination of mapsand tabular information that is stored and handled in a computer. The system can handledata linked to a geographical position. This link means that every spatial object in thedatabase has one or more coordinates in a system, which gives position on the earthsurface (Eklundh, 1999).Eklundh (1999) further states that the spatial objects are presented in either vector orraster format. Vector is a format where geographical objects in a coordinate system arelinked to attributes stored in tabular form, which describe the geographical data (seeFigure 3.1 a). A road can for example have information stored about its length andwhether it is gravel or tarmac etc. Raster is a format where every picture element (pixel)or cell is given a numeric value. This format is most commonly used when analyzingcontinuous surfaces, for example elevation (see Figure 3.1 b).(a)(b)Figure 3.1Vector (a) and Raster (b) layers representing reality.Source: www. giscentrum.lu.se.The most common demands on a general GIS can according to Eklundh (1999) beconcluded into a number of points:o Input and output of data: The system should be able to read data from a number ofdifferent sources such as maps, satellite and aerial data, GPS receivers and tabularinformation from field surveys. In order to read the input data, 1) the user must13