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So over the years working with elevation and image rasters in various formats I always kind of ignore the value of No Data. I usually just let the software/vendor/someone else decide on the value for me. Lately I've been giving it some thought. Why am I using this arbitrary software assigned value of:

  • -3.40282306074e+038 (I assume the lowest possible float number)
  • 255,255,255 (white)
  • 0,0,0 (black)
  • -255

Now I'm in a large process of organising and optimising our raster datasets. These datasets are elevation, analysis and aerial photography. And I am finding now is a good time to set a consistent No Data value. Personally I am thinking of using the following:

  • Elevation: -1
  • Air Photography: -1, -1, -1
  • Analysis: -1 (when possible, does not work for all datasets)

Concerning Elevation and Air Photo raster, will setting -1 really mess up analysis done on the dataset, will it display properly and does No Data really even matter?

I've done a few tests and everything seems to work out, but are there any long term implications that I need to worry about?

  • 4
    there are negative elevation (e.g. polders in the Netherlands, the dead sea...) so you should avoid -1. – radouxju Jun 15 '18 at 13:54
  • 1
    I'm in Ontario, so I really had not thought of that. It appears the lowest exposed land on Earth is at the Dead Sea shore, at -413 meters. So I believe I should adjust my -1 to a -1000. Thank you! – Cody Brown Jun 15 '18 at 14:08
  • 4
    Don't forget the more usual -9999 as a no data value. – Hornbydd Jun 15 '18 at 14:21
  • 1
    I´d say decide in situ: an actual value may be taken into account for any statistical analysis if not specified while NoData may not be supported by all formats/tools, both have advantages over the other in terms of visualization and so on. – ThingumaBob Jun 15 '18 at 14:43
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    And don't forget there's more to NoData than just values, you can also have alpha channels/mask bands ;) – user2856 Jun 21 '18 at 8:15

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