[OSM-talk] TIGER cleannup

[Beej Jorgensen]

Paul Fox wrote:
> but the fact that it seems the tiger maps show every old farm-trail 
> or track that's ever existed in the last 400 years, even if it's been
>  impassable and unmarked and on private property for 150 of those 
> years.  :-)

So true.  A track in northern California that was popular about 50 years
ago but is now virtually impassibly overgrown with sage is still marked
in the census data.

It's not just us who are fooled, though.  Google has footpaths marked as 
road, as well.

> you might be right.  it's certainly the path of least resistance. :-)
>  i'm very new to OSM, so i don't have a feel for what can and can't 
> be done readily.

I definitely *might* be.  :-) The amount of work to clean the census
data is absolutely gigantic.  I've corrected thousands of points in my
home town and some surrounding cities (all one sprawl) and it's taken
many many hours.  But with the number of OSM editors growing like mad,
and I managed to largely singlehandedly correct the data for an area
with a population of something like 120,000 people.

> i was hoping that somehow changes to certain kinds of imports could 
> be marked, and somehow "reapplied" to new data.  that all assumes 
> that lines/streets/etc all maintain their identifiers from one import
>  to the next.

Yes--I don't know how true that is.  Could be the ID doesn't change in
the data, simplifying matters, but it still is a tough problem with new
roads, changed intersections, data that is incorrect in the census and 
has been subsequently corrected by OSMers... :-(

Andy Robinson wrote me off-list concerning the accuracy of Yahoo and
Landsat images, putting them at about 30 meters and 90 meters,
respectively.  Pretty icky.  The number I remember off the top of my
head for census data is 40 meters.

Every time I've used the USGS DOQ and urban areas images (I get them
from terraserver--it's all public domain), they have aligned over my GPS
tracks basically exactly.  I haven't seen a mismatch with hundreds of
tracks in various areas.  The DOQ photos are really quite old, so it's 
sometimes tough use them to correct data, as the roads have changed.

If there are mismatches in the US with the USGS photos, I'd naturally
love to hear about them. Just to be safe, however, I have only been 
working in areas I frequent and for which I have a smattering of GPS tracks.

-Beej