[Imports] NHD Duplicate data

[Emilie Laffray]

2009/9/10 Mike N. <niceman at att.net>

> Doing a routine pre-upload checklist, I found a case where there was a
> large
> section of duplicate river overlap in adjacent NHD water basin extracts.
> This was the Mackinaw river in sub-basins 07130003 and 07130004 .    This
> becomes easier to see by loading the entire upload into JOSM - the
> 'flowlines' create a scatter plot that roughly follows the borderline on
> the
> NHD download map.   But duplicates extend for a long distance outside the
> primary sub-basin boundaries as indicated by the flowlines.
>
>   I'm not sure what the best solution is; a program to detect duplicate
> areas may not detect duplicates from an adjacent upload by a different
> person.
>

For the Corine import of France, I have been using Postgis and some SQL to
calculate overlap between two surfaces. It is a mixture of ST_Area with
ST_Intersect. It is not perfect but we caught lots of existing forests
inside OSM so we didn't have to upload them.

I am not exactly sure what your problem is but we could have a look.

Emilie Laffray
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