Ancient world base map tiles

Pleiades isn't a mapping site, but we have a few maps. There is one small scale map showing recent activity on the site currently centered on Asia Minor, and one larger scale map showing the immediate neighborhood of every positively located ancient place. The maps are extremely simple, just three kinds of overlays and a base map layer, the Google Maps terrain base map. The positives qualities of the Google base map are: global coverage, good cartography, high availability, excellent detail (full resolution to better than 1:10,000, all we need for Pleiades), and generally favorable (for us) terms of use. On the other hand: modern transportation ways and borders and labels are burned in with no options to style them away, and the terms of use are changing to a less favorable state. Google has announced that advertisements will appear in new applications. Existing applications like Pleiades are exempt for now, but I assume the terms will change again in the future (Google reserves the right to change terms) and that we will be subjected to Gmail-style contextual advertising or prominent commercial place markers somewhere down the road. Ads are entirely inappropriate for Pleiades. I'd rather show a plain white background than an ad-smeared terrain base map. Eventually, we'll need a base map with more favorable terms of use and fewer modern artefacts. Other projects will too, and so I'd like to kick off a discussion of how we might collaborate on creating one.

I'm impressed by MapBox's Natural Earth Hypsometric and Bathymetry base layer. The data behind it is public domain and the software stack is open source. There's even some open source support for running the Mapnik tile renderer on Amazon EC2. One might extend it using more detailed elevation data to generate the extra zoom levels that MapBox doesn't host. Pleiades doesn't need to zoom in to street level, but needs zoom levels equivalent to Google Map's level 12 at least. I'm curious whether global tiles at these zoom levels are possible with the service's SQLite-based architecture. The company's $500 per month tile hosting seems pretty reasonable, especially if it includes hosting the highest resolution tiles. Hosting global high resolution tiles at 12-15 zoom levels isn't going to be trivial or cheap, that's for sure.

Mixing of modern and ancient tiles could be a good interim approach. We might use the MapBox hypsometry and bathymetry (for example, or another equivalent tile set) as a base map layer and then overlay custom tiles generated in a matching style wherever we have ancient GIS layers which differ from modern layers. This requires more analysis to identify the tiles at all levels that would be impacted by feature differences – mainly the removal of modern canals and reservoirs, but also some shoreline changes – but in the end requires many fewer tiles tailored exclusively for ancient world map users and less duplicated effort.