[Talk-us] TIGER Data in Wrong Place

[Dave Hansen]

On Wed, 2009-05-06 at 19:08 +0100, Andrew Ayre wrote:
> Hi! When I load OSM data into my GPS unit using mkgmap for a place in 
> the UK then it is accurate. When I load OSM data for Tucson, Arizona 
> then it is off by perhaps 100ft.
> 
> I would like to make the maps for Tucson usable, so my questions are:
> 
>    - how do I tell where this problem begins and ends?

You probably can't do this on a large scale.

>    - how do I fix it?

In JOSM, you can select and move large numbers of objects at once.  My
neighborhood was off by a couple hundred meters.  I went and fixed it
all back up manually.

> I don't have the time to manually move everything, so there must be some 
> kind of automated solution? Does this problem exist for the whole of the 
> US? Is it well understood?

No, it doesn't exist for the whole US.

It is well understood.  TIGER is a collection of data from many, many
sources.  Some of these were from local governments that were themselves
aggregating data from multiple sources.  Sometimes, the data were off
from one of these sources.  It was not collected for the sole purpose of
mapping, so nobody really cared.

> Also if you look at the diagonal (NW-SE) part of the Arizona-Mexico 
> border there are streets in the US that appear in Mexico - the whole 
> border area appears to be a mess. How do I know what needs to be done to 
> fix this? The error looks larger than 100ft.

You really need some good GPS traces of the streets, or you can try to
align it on yahoo imagery.

-- Dave