[Proj] latlon projection

[Pavel Hančar]

  Hello,
I am trying to understand some basic concepts of map rendering, but I've
got really confused by the fact, that "longlat" or "lonlat" are often
mentioned as a name of a projection. For example:
+proj=longlat +datum=WGS84 +no_defs

AFAIK longitude and latitude stay for a coordination system, not for a map
projection. Thus I thought it was a kind of simplification and the actual
projection must have been the Equidistant Cylindrical. But I found the
Equidistant Cylindrical being determined by "eqc" not "longlat".  So what
is the "longlat"? I ended up running `proj -lP`, but found just this:

lonlat : Lat/long (Geodetic)
latlon : Lat/long (Geodetic alias)

The only explanation is, that it is geodetic. But to me it seems it is not
any explanation, but a further specification saying it is not geocentric,
but the angles are taken from normals of the ellipsoid.

So, what projection is the "lonlat"? Or how are longitude and latitude
projected to the flat map when nothing else is specified?

 Thank you very much.

  Best wishes,
  Pavel Hančar
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