[Talk-us] parcel data in OSM

[Michael Patrick]

> ... We have decided that we don't want parcel data into the US OSM
database.  ... looking at the map in Mass, the situation is not so cut and
dry. The open space layer from MassGIS was imported several years ago. This
has encouraged people to map out many of the hiking trails. ... So the
question is, what should the exact criteria be for including an
"open space" parcel in OSM. Consider some of the various types of
property.

Some general comments on including / excluding 'parcel' data.

The TIGER (Ref: The US Census Tiger FAQ
<http://www.census.gov/geo/www/tiger/faq-index.html>and TIGER/Line
Shapefiles Technical Documentation
2012<http://www.census.gov/geo/www/tiger/tgrshp2012/TGRSHP2012_TechDoc.pdf>)
import has established a de facto 'base map', along with all the
associated issues ( 2.4 Spatial Accuracy of Linear Features, 2.5 Initial
Sources, 2.6 Coordinates ) - "*average* of 7.6 meters (25 feet). In urban
areas, right of ways can commonly be 25 feet, The 'average' means some are
50ft or more, depending on the original source materials and MTAIP updates.

As was noted, the parcel information readily provides boundaries for open
space, but also, in most jurisdictions, the access to those open spaces,
i.e. easements. For instance, here in Seattle there are many shoreline
points that appear as somebodies lawn, but are are really public property.
Also there are many trails which connect through power line rights of way.
An additional factor is that fences lines, hedges, tree lines, etc.
invariably fall on or very near the property lines - and it's unlikely
someone with a GPS is going to traipse through these deliberate barriers to
get the data into OSM.. In urban and suburban areas, zoning requires
definite minimum setbacks which improve the checking building footprint
placement.

While accuracy and availability varies across the US, if a jurisdiction
does public property line data, despite all the disclaimers, the boundaries
are really good - because the jurisdiction usually uses it also for
producing notifications for property owners for permit activity and tasks
like laying fiber or digging around a pipeline. ( Read the Metadata to be
sure). Additionally, some areas knock out the road right of ways, and/or
provide center/lines.So the parcel data as property description reference
may not seem relevant to OSM, it directly supports the creation of a large
number of other OSM data for walk-ability maps, and the possible adjustment
of the somewhat iffy TIGER data. Even if the jurisdiction did the
absolutely easiest and cheapest method of rubber sheeting vectors from
scanned paper documents to local cadastral / PLSS data (benchmarks),

IMHO, having the parcels available increases the motivation to correct the
TIGER roads where needed.

And if we are looking for 'hooks' to ease the entry into OSM for newcomers,
being able withing seconds to identify their own home and those of their
neighbors is absolutely huge - something they are familiar with and know
intimately. Every time I've used the tax assessor's application with
someone looking over my shoulder, it sometimes ends up being hours before I
can pry them away. Every neighborhood project, grant application, community
action meeting, etc, has the parcel layer as the fundamental layer -
because all the covenants, regulations, permits, etc. center are attached
to it.

Michael Patrick
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