Geographic Information Systems Notes

In 2014, CPTR 521 used Pro Spatial with SQL Server 2012 to study spatial data in SQL Server 2012. This page documents that experience.

Spatial Reference Systems (SRS)

• Spatial Reference Systems - coordinate system to identify particular points on the earth (e.g. WGS84)
• geoid - the word used to describe the shape of the earth.
• reference ellipsoid - a smooth model used by scientists to approximate the shape of the earth.
  • oblate spheroid - most commonly used reference ellipsoid
  • Most reference ellipsoids aren't meant to model the entire earth, but some such as the World Geodetic System 1984 do.
• SQL Server 2012 recognizes spatial reference systems based on a number of different reference ellipsoids.

The above table demonstrates the Size/Shape characteristics of a SRS.

To complete the package we need reference points to place the ellipsoid in the correct position relative to the earth.

Definition [Spatial Reference System] A geodetic datum is made up of a reference ellipsoid and a set of reference points to position the ellipsoid relative to the earth.

Geographic Coordinate Systems

• Latitude - 0 degrees at equator, 90 degrees at the north pole, -90 degrees at the south pole.
• Longitude - 0-180 degrees east or west of the prime meridian

Projected Coordinate Systems

Because we carry maps on flat surfaces (instead of geoids), the area of the world that we want to see on the map needs to be projected onto the Cartesian coordinate plane.

• Conformal Projection - any projection that preserves the local shape of objects on the resulting map.

• Mercador projection is such a map projection and is used by Bing and Google maps.

Universal Transverse Mercator Projection is a grid composed of many projections laid side by side. Globe is sliced (north/south) into 60 strips (of 6 degrees each). Each strip is divided at the equator. E.g. Chattanooga, TN is in Zone 16N.

Projection Parameters