Whats the deal with coordinate systems and map projections?
It turns out that there hundreds of coordinate systems in use today. In the general sense that’s ok, but if you try to overlay a streets layer in one coordinate system with a rivers layer in another coordinate system, they will not line up. Each layer may be just fine independently, but you can not compare apples to oranges. GPS natively returns a position as a Latitude and Longitude referencing the WGS84 ellipsoid (for you geodesy minded folks, WGS84 and NAD83 are functionally interchangeable down to better than a meter in most cases). If the maps you wish to use for AVL reference a coordinate system that is not in a latitude and longitude format, something has to be transformed – either the GPS coordinates have to be changed or the maps have to be changed to make both sets of coordinates line up.
