Data Needs should describe projection requirements for spatial data

[davemfish]

There is the projected property of an arg:

"lulc_path": {
            **spec_utils.LULC,
            "projected": True,

And then there is the different_projections_ok property:

"args_with_spatial_overlap": {
        "spatial_keys": ["dem_path", "erosivity_path", "erodibility_path",
                         "lulc_path", "drainage_path", "watersheds_path", ],
        "different_projections_ok": False,
    },

We're not referencing either of these right now. If we do, I think it would require a bit more explanation, rather than just rendering the values of those properties.

For example projected: true might need to read: "This layer must use a projected coordinate system (as opposed to a geographic coordinate system)."

And different_projections_ok might translate to a statement like, "spatial layers must all use the same coordinate system", or "spatial layers may use different coordinate systems so long as all layers have a well-defined coordinate system".

I don't think we need a statement about args_with_spatial_overlap -- it kind of goes without saying.