I've been trying to find some easier ways to clean up the Tiger data for my area around Portland, Oregon. I've been corresponding with a few others also trying to do the same thing.

I'll skip to the punchline first: Better JOSM layers for aerial photos at

http://terraservice.net/ogcmap.ashx?version=1.1.1&request=GetMap&Layers=urbanarea&Styles=&SRS=EPSG:4326&format=image/jpeg&

and public street maps from the county tax office at

http://columbo.nrlssc.navy.mil/ogcwms/servlet/WMSServlet/Portland_OR_Metro_Maps.wms?VERSION=1.1.1&REQUEST=GetMap&SRS=EPSG:4326&LAYERS=0:42&FORMAT=image/png

Here's the long version of the story:

For my county, I've found excellent position consistency among all data sources other than Tiger. My GPS readings match the Yahoo aerial photos, Google Earth, Washington County tax maps, Beaverton city maps, and the USGS urban area photo maps at terraservice.net. The Tiger data is broadly correct with pretty much all the right streets in the right relationships, but it is often shifted out of place by varying amounts.

So everybody agrees except Tiger. This is good, in that it gives me confidence in the other sources, meaning I don't have to travel every single street with my GPS since my tax dollars already did so. I figure that if I get a large rectangle by GPS which matches the aerial photos, then the area within the rectangle can be aligned with just the photo. I've been looking for the most efficient way to do that. Sometimes the Yahoo aerial photos are not as clear as I would like, such as being obscured by trees.

Although I like the simplicity of Potlatch, I found I really need the multiple-node selection and movement capability in JOSM for realigning the Tiger data. The key, then, has been to find better sources of public data which I can use as WMS layers in JOSM.

The first was better aerial photos. I don't copy from Google Maps or Earth, but I do occasionally cross-check things there. I noticed in Google Earth that the on-screen credits do change, and seem to reflect the actual source of your current view. I found Portland, OR credited for close-up aerial street photos. Digging around some more, I found that this data is being distributed by the USGS as part of its urban area focus project, and I stumbled into this page:

osm.wiki/index.php/User:Beej71

showing how to use it as a WMS layer in JOSM. Item number one (better photos) solved.

Item number two took longer to figure out. I've used the Washington County tax maps at http://washims.co.washington.or.us for several years for personal use, before I found OSM. I have seen references on the county web site to ESRI and ARC software, so I knew there was a decent base underneath. The one thing I could not find was any WMS services.

I spent some time with PDF maps, and hit a dead-end with MetaCarta's currently-broken map rectifier :-( This sent me hunting again back closer to the source. I eventually Googled into a Navy project which is a WMS server for many GIS sources, at

http://columbo.nrlssc.navy.mil/ogcwms/servlet/WMSServlet

With some WMS experimentation in Google Earth, I was able to find what I was seeking: decent street maps from the county tax assessor at varying levels of resolution. Quite excellent resolution, in fact; the details increase as you zoom in closer to the street and lot level. Problem two solved.

Although I'm focusing on one particular county, it appears that the Navy project has hundreds or thousands of data sources available. If your county data is there, it may be worth a look.

I understand that we need to be very cautious about copying other people's intellectual property into OSM. In this case, since the data is based on public records from my tax assessor's office, I don't expect there is a problem in using it as a verification base for the Tiger data.

The only minor problem I am having is that the Portland tax maps have light grey lines on a white background for the streets, and the mappaint mode in JOSM is hard to see on top of it. Switching to wireframe mode is an adequate workaround for now.