The importance of knowing about the Datum recently came to my attention as I was working with GIS data on a Language Documentation project. We were collecting GPS coordinates with a handheld GPS unit and comparing these coordinates with data supplied by the national cartographic office. End goal was to compare data samples collected with conclusions proposed by the national cartographic office.

So, what am I talking about?

GIS data is used in a Geographical Information System. Basically, you can think of maps and what you might want to show with a map: rivers, towns, roads, language features, dialect markers, etc. Well, maps are shapes superimposed with a grid. And coordinates are a way of naming where on a particular grid a given point is located.