On Wed, Jan 27, 2010 at 8:47 PM, David ``Smith'' <vidthe...@gmail.com>wrote:
> Since some people consider > the entire "layer" tag to be "tagging for the renderer" these people > probably don't think it's important to add thorough layer information; > I would agree with your disagreement with such people. But I understand their confusion. The *naming* of layer=* is unfortunately renderish, but it carries real meaning beyond the oldschool mapmakers' plate masks. I would wish the tag:layer had been more abstractly named tag:level. ah well. I would also prefer real altitudes on all points rather than ordinal relative levels (whether misnamed layer or not), but that's a bit of an ask. And would cause semantic problems when ways become buildings (foundation or roof elevation? include vertical segments?). Ordering of the bridges in http://www.stockphotopro.com/photo-thumbs-2/stockphotopro_33168BXD_no_title.jpgfrom top-most to bottom-most is Data. Likewise ordering of tunnel ramps weaving out of our Big Dig is Data. It is DATA that a Transit line is in a uncovered ditch even when it's not under a bridge. Some non-rendering data-using software (or a person using data access) will want to know up from down. Silly example -- I could write a script to find examples of various topological knots in the interchange ramp network, and which is under or over at a crossing is critical. Truck routing really need to know headroom at each underpass too, but we don't have that usually. -- Bill n1...@arrl.net bill.n1...@gmail.com
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