What strategies, criteria, or rules do you use for selecting coordinate systems for
- (a) storing,
- (b) analyzing, and
- (c) displaying GIS data?
(I humbly offer my reply to a related question about watershed analysis as an example of the considerations involved in (b).)
What are the pitfalls to watch out for?
Links to Web sites you find particularly helpful in this regard are welcome.
Answer
a. It is good practice to store a version of the data in the projection in which it was captured. Re-projection can be a lossy process, and it is important to have the original. I have a preference for storing in WGS84 for the sake of simplicity.
b. Depending on your software you may need to re-project into a metre based projections such as UTM. Support for native geodetic is being added (PostGIS, SQL server). For raster analysis it can be preferable to keep the data in the format it was supplied to avoid data loss through interpolation.
c. Web mapping systems have standardised on spherical mercator, and to overlay tiles they need to be in this projection. For overlaying vector on google maps you use WGS84. If you are not targeting web mapping there will usually be a local projection that is standard.
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