New Datum for North America

Before I get off the datum topic, I want to share a little bit about what datum the National Geodetic Survey (NGS) is moving towards. The NGS is a part of NOAA, the National Oceanic and Atmospheric association. If you use for anything, you’re familiar with the outputs from NOAA.

The current official datums used by NGS are NAD83 (learn more in the last post) and NAVD88. Briefly, NAVD88 is a datum that uses gravimetric measurements. It’s considered a vertical datum, mostly used for mapping elevation. NAVD88 is defined for the contiguous US and Alaska, but other parts of the US use a different datum.

The replacement for NAVD88 is called GRAV-D and will be in place by 2022. NAD83 will be adjusted and updated. Learn more about those changes here.

One of the things to keep in mind regarding datums is that their error is not constant across the whole globe. Knowing where the error occurs can help you pick a more appropriate datum for your project. The move from NAVD88 will be barely noticeable in Florida, but Colorado will have a number of peaks lose their 14,000 foot status. This is a nice article from Coloradan Alumni Magazine about the GRAV-D rollout from the prospective of a state expecting a fair deal of change under the new datum.

What should you do with this information? If you’re mapping anything or recording coordinates between now and the rollout of these new datums, record your metadata. This will make converting data easier, and converting data will be necessary to project old and new data together.

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