Do you know what a Geoid is?

I’ve been working my way through Beginning Spatial with SQL Server 2008, actually “through” is an overstatement. I’ve been working through chapter 1, which is full of a lot of theory about spatial data and coordinate systems.

The book talks about the issues of determining where a point on the Earth is. Apparently there are all sorts of ways to project the Earth onto maps, how to calculate angles, account for the shape of the earth, etc.

Apparently the earth isn’t a sphere. I thought it was, and when I asked me kids, they said the same thing. So you can’t model the earth very well with a sphere.

Turns out an ellipsoid doesn’t work as well, either. Ignoring the terrain and topography, it still isn’t the best model. So a geoid is used, which is something I’d never heard.

It’s a model of a surface of equal gravitational potential. You can read about some of the hassles and theory in this white paper on spatial, which seems even more complicated than the book.

I’m a math guy, 8 or 10 semesters of calculus and advanced math in my college career, and this stuff is interesting to me. But it’s hard.

I’m not sure how much you need to learn to work with spatial in SQL Server, but it is interesting to learn a bit about the theory. I’m in Chapter 2 now and looking forward to more.