[Imports] Baltimore County Maryland Hydrology Import

[David Jackson (OCTO)]

Elliot,

Great work on the Baltimore county building & address import.  I have local
familiarity with the county and your work looks excellent.

David

David Jackson   |  GIS Analyst  |  Office of the Chief technology Officer
 (W) 202.724.5135  |  200 I ST SE,  5TH FL,  Washington, DC
davidy.jackson at dc.gov |   Blog:  dcaddresscoordinates.blogspot.com
Telework Day: Fri


On Fri, Sep 5, 2014 at 10:32 AM, Elliott Plack <elliott.plack at gmail.com>
wrote:

> Now that the building and address import is complete, I am moving on to
> some of the planimetrics that make OSM look good but also contain useful
> information. Parts of the county have a very good, dense network of
> streams, traced by a few users, but it can be difficult to spot some
> streams amidst tree cover on air photos. In these areas where hydrology
> (streams, rivers, ponds, storm water management, piers, etc) exist, I am
> proposing to import public domain Baltimore County hydrology, while taking
> care not to overwrite anyones hard work.
>
> Before I write up a wiki, here are the basic details:
>
>
>    1. I made a model that simplifies the polyline hydrology feature class
>    with a simplification factor of two feet to prevent "overnoding". In
>    experimenting, two feet between nodes keeps the data simple on the map, but
>    typically doesn't result in it looking too jagged. The source data is drawn
>    with a digital pen and then converted to polyline, so any given 10 foot
>    segment might have 500 nodes in the source.
>    2. I ran Paul Norman's ogr2osm on the result from step one, with a
>    custom translation to convert the various feature types in the source data
>    to something compatible with the OSM key/value data model. Here is that
>    translation: https://gist.github.com/talllguy/52066d13d323f1535f3a
>    3. Here is the resulting OSM file of that translation:
>    http://1drv.ms/1lLHSIm
>    4. In JOSM I look for a stream system that is missing. I disconnect
>    the last segment that would intersect an existing water feature already on
>    the map, like a river or coastline. I use the 'select all connecting ways'
>    tool to select the entire system and then copy that to a new layer and
>    download existing OSM data to that layer. (some tags are purposefully
>    translated with no type, so I have to go back and correct them individually
>    and check the data)
>    5. I run the validator to look for issues. Null names, and nodes that
>    don't quite connect are easy to find this way.
>    6. Upon solving all validator issues I import the system.
>
> Notes:
>
>    - I'm not going to mess with importing coastline. Our coast is pretty
>    good and there are too many ways to introduce bugs when importing coastline.
>    - Some of the features like boat docks, ramps, and piers may be too
>    complicated for import. Those I'd address individually and may just use a
>    node for leisure=slipway.
>    - For larger rivers where there is a riverbank in the data, I'll use
>    the approved water=* tagging.
>
> Questions:
>
> We have data on where the coastline is comprised of bulkhead, like where
> the coastline is unnatural. Is that relevant to the project? I haven't seen
> a bulkhead type tag but it could be considered a seawall.
>
> As a test, I uploaded a small stream system that had not been traced at
> all, the Sawmill Branch, so you all can see how it'd look on the map. That
> system is here: http://www.openstreetmap.org/#map=15/39.5217/-76.5440
>
> This is will be a very manual process and as a steward of open data, I
> will take great care not to undo other mappers hard work.
>
> --
> Elliott Plack
> http://about.me/elliottp
>
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>
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