Imagine unpeeling the skin of an orange and trying to flatten it out onto a flat surface - it's impossible to flatten it without distorting the shape or area of the skin's surface. In order to overlay two or more layers, the layers must be in the same projection. Map scale is the relationship between the dimensions of the geographic features in a map and the actual size of the geographic object that they represent on earth. This is a number that is commonly expressed as a ratio or fraction. Spatial data represents the shape and location of the geographic features.
Spatial data is stored in a digitized computer file.
Thematic map is a map that symbolizes geographic features according to a particular attribute. Click here for an example. Click here for an example. There are many desktop GIS software programs currently on the market. These programs all offer mapping capabilities, but range in terms of their computer hardware requirements and spatial analysis capabilities.