I have been supplied a map of spot elevations by a client that somebody else (gov agency) prepared.
Anybody know the vertical datum this mapping tool uses? I haven't been able to find the documentation.
You may want to check here.
I would think it should be NAVD88, although I wonder if the accuracy of any of that data is high enough to make a difference? At least in the east, where the difference between NGVD29 and NAVD88 is usually under 25 cm.
> I would think it should be NAVD88, although I wonder if the accuracy of any of that data is high enough to make a difference? At least in the east, where the difference between NGVD29 and NAVD88 is usually under 25 cm.
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Great graphic. Thanks!
I can't wait for our third datum in 100 years. That is going to be so much more helpful.
Thanks for the reply.
It does matter here... +3.74' (NGVD29 to NAVD88)
It was suggested to go for a LOMA in an area prone to ponding at the 1% flood. I think they trusted the USGS model and were comparing a vertical from a NGVD29 LOMA in the area with the NAVD88 elevations from the USGS viewer. They thought it would work out.
It did not, the FF is about 2.3' below the BFE from the previous LOMA (not to mention the crawl space).
Thanks Doug.
Not sure if you were being sarcastic or just not aware. The prediction for the next vertical datum is in 2022. Of course this really means 2030 if you go by track record that NGS has for the previous 2 datums. :-/
> Not sure if you were being sarcastic or just not aware. The prediction for the next vertical datum is in 2022. Of course this really means 2030 if you go by track record that NGS has for the previous 2 datums. :-/
Sorry, I forgot the sarcasm font.
Also, my apologies to Kevin for the thread hijack.
Here in central Indiana the roughly 0.4 feet difference in datums has caused more trouble than done any good, especially among confused local bureaucrats.
I wonder, will this become like Daylight Savings Time? Will our third adjustment carry us back closer to the 1929 datum?