Unified WMTS element support across backends

[philippjfr]

The WMTS element now supports the tile source URL format that is also supported by bokeh, finally unifying the two. This PR also deprecates Tiles since it does exactly what WMTS does. I'd also be happy to keep Tiles as a simple alias for WMTS though, @jbednar any thoughts?

Here's the same plot in two backends:

tiles = gv.WMTS('https://maps.wikimedia.org/osm-intl/{Z}/{X}/{Y}@2x.png') 

# Project data to Web Mercator
nybb = gpd.read_file(gpd.datasets.get_path('nybb'))
poly_data = nybb.to_crs(ccrs.GOOGLE_MERCATOR.proj4_init)
polys = gv.Polygons(poly_data, vdims='BoroName', crs=ccrs.GOOGLE_MERCATOR)
tiles * polys

[jbednar]

Great! The name WMTS has always been mysterious-looking, and I do think a better name would be good. Is Tiles the appropriate name? Are there WMTS sources that are not map tiles? If so it's fine; if not MapTiles might be a better name. I also like TileSource or TileServer, because the one thing that's important to know about Tiles/WTMS objects is that they are served by an external site, unlike just about any other Element.

[philippjfr]

TileSource/MapTiles seem reasonable, that said it would add a third alias, with the other two names (Tiles and WMTS) having to go through a fairly long deprecation cycle, so maybe I favor Tiles.

Are there WMTS sources that are not map tiles?

Don't think so since WMTS stands for Web Mapping Tile Service. Misread your question, I think the XYZ scheme uses the assumption that it's map tiles in mercator coordinates, so MapTiles might be more accurate.

[philippjfr]

I'm going to go ahead and merge once tests pass, please file an issue to add a TileSource/MapTiles alias and deprecate WMTS and Tiles if you think it's a better name.

[jbednar]

Misread your question, I think the XYZ scheme uses the assumption that it's map tiles in mercator coordinates, so MapTiles might be more accurate.

Right; my question was confusing, but what I was getting at was whether there are tile sources that our objects would accept that are not maps. Bokeh seems to allow for the possibility, in that it has a TileSource base class that does not mention maps. I believe that tiles have been used in Bokeh for spectrogram displays that are not maps but I suppose can somehow be made to fit into the XYZ format (as long as Y is unbounded, as it is time), and I want to make sure that (a) we don't rule out applications like that, and (b) we have names that correctly reflect the level of generality.

[jbednar]

(This being geoviews, we'd have to add a Tiles object to hv to handle such cases, presumably!)