Home > Geospatial, SQL Server 2008R2, SQL Server 2012 > Spatial, Geography and Geometry, oh my! – Part 2: Spatial Data (continued)

Spatial, Geography and Geometry, oh my! – Part 2: Spatial Data (continued)

Last week, we started the Spatial Analysis series with an overview of the two-dimensional aspects of geometry.  Today, we’ll look into coordinate systems, which include both two- and three-dimensional mapping.

The purpose of any spatial reference system is to uniquely identify and describe any point is space.  To describe positions in space, every spatial system is based on an underlying coordinate system.   A set of three coordinates (1,2,3) can therefore be used to describe the position of a point from an origin in three-dimensional space.  (Remember high-school geometry with X, Y, Z coordinate systems?  Me neither.)  There are many different types of coordinate systems, but when you use geospatial data in SQL Server, you are most likely using a spatial reference system based on either a geographic or projected coordinate system.

Geographic Coordinate Systems

In a geographic coordinate system, any position on the earth’s surface can be defined using two coordinates.  Latitude and Longitude, and Altitude.

Latitude is defined as the angle between the equator and a line drawn from the point to the center of the earth.  Longitude is defined as the angle between the prime meridian (Greenwich, England) and a line drawn from the point to the center of the earth.  Both coordinates are angles, and as such are referred to in degrees.   Altitude is quite simply defined as the distance measured from the point to the center of the earth.  With that distance, coupled with latitude and longitude, we’ll have a precise point in space.

Projected Coordinate Systems

A projected coordinate system, as opposed to a Geographic Coordinate System, describes the position of a point on the earth’s surface as they lie on a flat, two-dimensional plane.  Think of the Projected system as defining a point on a map, as opposed to a globe.  Since we’re projecting on a flat map, we can go back to using the good ol’ (x, y) coordinate system.

That’ll wrap up the defining spatial information.  Next up, we’ll take a look at applying these systems to the earth, and how to use them in SQL Server.  Tune in on Tuesday!

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  1. October 18, 2012 at 8:21 am

    This site was… how do I say it? Relevant!! Finally I’ve found something that helped me. Thanks!

  1. October 18, 2012 at 4:10 am
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