The Spatial Miscellany


A weblog. A website. A geospatial miscellany…

What’s your Lat \ Long?

The release of SQL Server 2008 will see two new types for representing spatial information, namely GEOMETRY & GEOGRAPHY. Geometry will be used for their planar (“flat-Earth”) model and Geography for their ellipsoidal (“round-Earth”) model, it’s a unique approach and seems to make sense, time will tell how popular it proves. Perhaps the most interesting difference between the two types reared its head on the SQL Spatial forum a few weeks back (see thread)…

When Microsoft released a preview of SQL Server 2008 in November, the order in which they returned coordinate pairs from one type, was the opposite of the order they returned coordinate pairs from the other type. The problem seems to stem from the widely held assumption that ‘What is your Lat Long?’ is the same question as ‘What is your XY?’

SQL Server - Round or Flat?

However, Latitude is a measure of distance from the equator, so it’s really more analogous to the distance Y in a planar model; likewise, Longitude is a measure of distance from the Prime Meridian and is therefore analogous to the distance X in a planar model. So ‘What is your XY?’ in a flat earth model, is really more comparable to the question ‘What is your Long Lat?’ in a round earth model. Traditionally GI professionals, and the software they use, have simply switched Latitude and Longitude, conveniently storing all coordinate pairs as XY…or Longitude \ Latitude.

There is a whole load more behind this issue than covered in the description above, check out the forum thread for a full brief. The good news is Microsoft have listened to the community, and indicated they’ll make efforts to switch the order before release; fingers crossed they can do this in time, and the spatial team has the priority to delay release if necessary. Their responsiveness earned a box of chocolates from Paul Ramsey; elsewhere, Morten Nielsen and Bill Dollins have a number of informed posts on SQL Server Spatial.

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