This piece is a raised-relief terrain map of Nantucket at 1:250000 scale, with 15:1 vertical exaggeration.
Purchase a finished ornament from my Etsy shop at
https://www.etsy.com/listing/476281806/nantucket-3d-printed-christmas-ornament
The source of the elevation data is the U.S. Geological Survey. The USGS home page is http://www.usgs.gov/.