Hello Dan Kane,
Unfortunately you cannot change the predefined zoom levels in the current version of RadMap, however, we are planning to improve this behavior for one of the future releases. Also, we are planning significant updates for the map tile provider logic and you can track the progress through our public issue tracking system
(note this PITS issue has different title, but we will implement ability to limit zoom levels (min-max) for map provider when we will be working on this task).
As for your second question -- RadMap does not use static pixel-per-meter or coordinate-per-meter ratio. It uses more complex calculations which involve geographical projections (most of the online map tile providers use Mercator projection). You can find more information about tile systems here
(this article describe Bing Maps Tile System).
the Telerik team
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