Chapter 3 lecture

This lecture kinda blew my mind; it was the first time I'd ever heard the word datum before (that I know of). So a lot of terminology and concepts were new and somewhat intimidating. But now that I've done the ESRI tutorial, read some in the book, and gone over my lecture notes again... I'm starting to get it. It really did take 3 times of pouring over the same information, but in different formats, for it to sink in. The sinking in part is exciting though, and here's a very brief summary of some things, but not everything.

Geodesy is the study of the size and shape of the Earth. Sounds simple enough- but it's not! There are spheroids and ellipsoids involved (apparently the same thing) which are smooth mathematical models of the Earth, while a geoid is a geographic model of the Earth which approximates gravitational pull. Datums are a set of coordinate locations which have been measured horizontally or vertically and tell us the latitude and longitude of a set of points on an ellipsoid. Also called a reference surface. Some common ones are NAD 27 and NAD 83. Projecting maps is whole other monster which always involves distortion of one or all of these: shape, area, distance, and direction. Here in the US we are likely to use either the Lambert Conformal Conic or the Universal Transverse Mercator projections. Counties often use State Plane as their projection of choice. North Carolina only has one state plane, but many states have more than one. Now I need to study for tomorrow's test...