Surface Analysis (Hillshade / Slope / Aspect / Contours etc)
Justing seeking some information as to the best method for undertaking surface analysis using a DEM. If the DEM is in geographics should it be reprojected before any analysis. If yes, what is the best projection for NSW Australia when working with a DEM that covers three Zones. Should we use Lambert, Albers etc do the analysis and convert back ???
Analysis types are hillshade / contours / aspect / slope etc.
Note the DEM is already mosaic. It is a state wide coverage
Mapping Center Answer:
For an area the size of Australia, a strategy regarding the types of distortion projections cause (areal, shape, and distance) is needed. Conformal projected coordinate systems, like Lambert and Albers, sacrifice on all types of distortion--but provide a good visual portrayal of a large area of the globe.
Depending on what analysis you need, you might favor an equal-area or equi-distant projected coordinate system. Of course it's now bloomin' obvious that our folder of continents (in the predefined projected coordinate systems) is not all that helpful for Australia!
However, the principles applied to the other continents still apply. The Central meridian and standar parallels must be optimized for Australia. If you look in the South America folder, there is an equi-distant and an equal-area option.
Given that you've mentioned (earlier) about wanting to use slope, and then zonally analyze it, I think a good argument can be made for the equal area coordinate system. Test it though, as you may want additionally project it to a conformal projection for cartographic purposes, and the purpose of the test is to verify that no artifacts from the projection algorithms are obviously introduced.
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