[R-sig-Geo] measuring longitudes as if they were parallels?

[john d]

Dear all,

Here's another issue that I've been struggling with and I'd really
appreciate any input.

I want to compare the latitudinal and longitudinal extents of different
shapefiles. Comparing latitudes is straightforward because they are
measured as parallels, so they are "self-referential". However, measuring
longitudes is always tricky because, as they are represented as meridians,
longitudinal degrees always depend on their latitude.

Is there a way to represent longitudes that is also self-referential?
Perhaps some transformation?

Any discussion in this respect will be greatly appreciated.

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