GIS Tips: Avoid Projection Distortion in your Geodatabase

A few years ago I was lucky enough to be involved in the Crown Estate (TCE) Round 3 discussions on how to regulate the influx of geospatial data they would recieve upon the end of the Round 3 wind energy projects here in the UK, this was due to the stipulation that the geospatial data used within the project needed to be “handed over” to TCE for review and inclusion in their MARS system.

One thing that shocked me was that their advice to each of the project GIS managers to use the relevant WGS84 Universal Transverse Mercator Zone relevant to their project, for example, the Zone 7 project near the Isle of Wight project in the UK was to use UTM 30 North.

Why did it shock me? Well, for several reasons – firstly, you must understand the basic principles of Tissots Indicatrix and the potential for projection distortion when using offshore data for an area larger than 1 degree (Laterally and Longitudinally) and all of these projects would have to deal with multiple geospatial data sources (geophysical survey, geotechnical survey, air quality analysis and tide to name a few). So what would happen when all the gigabytes of data started rolling in and the multibeam (MBES) data was recorded in WGS84? Or what to do with the aggregates data stored in OSGB36?

ImageNow, lets be clear, the advice from TCE was geospatial data should use the relevant UTM zone, it did not explicitly define that it MUST be used or provided in this format. Only problem was that the more of the data managers I spoke to on this, the more it became apparent that they had taken the information as gospel and had started to store their data in UTM zone projection systems.

I suggested this and I suggest it to you now, for Offshore geotabase storage and for general work, use WGS84, no projection, just plain old WGS84. This way you won’t have to worry (too much) about your distortion over several degrees and you definitely won’t have to worry about your accuracy or precision.


Okay, I can hear the purists shout “but you can’t measure areas in WGS84!” and you are, of course, right (well, kind of, you can always do your own calculations!). For presentation of data in maps or figures I wholly recommend using a projection and for calculating areas you must use a projection system, but the use of the projection system working in this way is kept to a minimum and there is less chance of building upon the distortion already created by said projection.



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