This is a related (on a lower level) to my other question. Are there any open datasets that contain latitude, longtitude, and an indicator of whether or not the point is land or water? The resolution doesn't need to be that fine (maybe 0.01 decimal degrees?).

There are some datasets that work with ocean coastlines, like the NOAA data, Natural Earth, or Landscan, but the latter is proprietary, and I don't think the first two include all water. Just oceans, from what I can tell.

If data like these are available, my plan is to create a connected graph of latitude/longitude "water cells" and use that and a shortest path algorithm to create an extremely rough estimate of distance between two points.

EDIT: I should clarify that I'm interested in a dataset that's worldwide, not just for one specific country or body of water.

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    Have you tried using openstreetmap.org? I was going to suggest usgs.gov topographical data (high resolution), but realized that water isn't always at sea level. On the other hand, it might be worth a quick look. – Barry Carter Aug 7 '16 at 0:16
  • @BarryCarter I'll look into openstreetmap. Is it worldwide? I'll edit the question to make it clear that I'm not only concerned with a certain area. – Michael A Aug 8 '16 at 12:55
  • @MichaelA. OSM is a global dataset. What software do you plan to use? Are you looking for a raster or vector format? – dof1985 Aug 8 '16 at 18:42
  • @dof1985 I'm not looking to use any GIS software, and I'm not making any maps, so raster or vector is orthogonal to my needs. My plan is to create a connected graph of latitude/longitude "water cells" and use that and a shortest path algorithm to create an extremely rough estimate of over-water-distance between two points. Any format that Python could read easily (csv, text, etc.) is helpful. – Michael A Aug 8 '16 at 19:16
  • @MichaelA, as far as I know the data you are looking for may be found as grd, ascii or Geotiff (aka raster, which are at the bottom line all text based files). These however may need some pre processing. Additionally some vector data is available under the .shp format (Land polygons in the website of DIVAGIS). Both however would require some pre processing to provide what you are looking for. – dof1985 Aug 9 '16 at 6:32

You can search for a ‘global water mask’

Here is one at 250m resolution from the Global Land Cover Facility (GLCF) at the University of Maryland based on data from the MODIS satellite:

http://landcover.org/data/watermask/

citation: Carroll, M., Townshend, J., DiMiceli, C., Noojipady, P., Sohlberg, R. 2009. A New Global Raster Water Mask at 250 Meter Resolution. International Journal of Digital Earth. ( volume 2 number 4)

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