Why is it useful to store data in unusual projections and datums?
I understand the value of projections as output constructs, because of distortion, etc: that much is justifiable.
However, I don't understand why, for instance, states use state plane projections in data. We have decimal accuracy: why not just store precise values in EPSG:4326? Is this entirely a remnant of pre-auto-reprojection days, or is there a value proposition I'm missing?
I'll restrict the scope of this question to vector data only to make it more concrete.
Answer
Legacy. Back in the Day (and now too) it was/is (much) easier to write a system that works in cartesian space instead of spherical coordinates relative on a spheroid. (What's the distance between A and B on a plane? over the surface of a sphere? of a spheroid? do you feel the degree of difficulty increasing?) And since most counties/states/cities exist in limited geographical areas that are amenable to fitting into map projections, it made sense to store and work with their data in cartesian coordinates in a local map projection.
No comments:
Post a Comment