[Talk-us] hydrology Alaska

Christoph Hormann osm at imagico.de
Tue Oct 17 14:03:22 UTC 2017

On Tuesday 17 October 2017, ANT Berezhnyi wrote:
> so on the question ...
> Is it possible to vectorize the USGS on the OSM if there is no
> Landsat, and everything else in the clouds, or in the snow, or the
> quality is bad ...

There are no parts of the US where there is no better imagery available 
than the 15 year old Landsat Geocover background image in Bing.  Most 
of Alaska is now covered by high resolution images in at least one of 
the available imagery layers (Bing/Mapbox/DG/ESRI).  And where this is 
not the case or images are unsuitable you will be able to find newer 
Landsat or Sentinel-2 images.  If you have troubles finding a suitable 
image for a specific area just ask - someone will likely be able to 
point you to them.  The Russian community has used open data images for 
quite some time in remote areas of the north.

But no image, no matter how suitable it is for the mapping task at hand, 
absolves you from carefully verifying what you map.  Tracing helper 
tools like scanaerial do not do this for you.

Old USGS maps are useful for names and as hints to interpreting imagery 
but should never be used for tracing geometries - they are just too old 
for that in most cases.

And as Ben Discoe pointed out you need to adjust your methods of tracing 
water areas, Something like https://www.openstreetmap.org/way/532622119 
is just not a good geometry representation (lots of nodes but with 
coordinates rounded to an arbitrary pixel grid is just wasteful).

Christoph Hormann

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