which is better?

General talk
1

Which is more accurate for positioning on map?

The GeoBase / Tiger import or the yahoo sattelite background image?

Is the yahoo imagery aligned with the map really well (in Potlatch)?

In some areas the Yahoo imagery is almost useless as it is such low resolution (like around my home town) in others it is really clear.
But the the geoBase or Tiger import seems to be off by up to a kilometer in some spots and bang on in others.

Also sometimes the GeoBase/tiger import is really well done (maybe even OVER done… 100+ nodes for a few kilometers of slight curve in highway)
and in other areas it is a mangled mess of bits of road.

Last night I came across an area that had lots of duplicate highways that were not obvious at first as they almost lined up with eachother perfectly. (Nanimo)
I struck a balance between which duplicate map had more information, less errors, lined up with yahoo, lined up with GPS tracks, etc, and then deleted the other. I made sure that whichever i used merged with the other properly.

If I deleted someones many hours of work, I am sorry, but I chose which had the best and merged everything into one map.
I would imagine a GPS unit or other future application trying to use the data as it was before would have an anuerysm trying to figure out routing.

2

As you note, the most accurate positioning will depend on the location - in the US, it appears that some Tiger data was based on underlying survey data, while others were created from an estimate. I have seen some Yahoo imagery that needed adjustment. Even a consumer grade GPS making several tracks is more accurate than both aerial imagery and Tiger data if nothing else is known.

Some purists might say that no editing should be done without an accurate GPS reference. But if no GPS reference is possible, and there is a good reason to correct the road, I would say to follow the Yahoo imagery. A good reason would be to fix tangled roads to create a routable map, especially if you have first hand knowledge of the area from having traveled through it.

3

Thanks,

Basically I’m trying to combine the best of all sources available.

There are spots I have come across where none of the sources agreed with each other, so the changes I made were minimal to make the road routable or make sense.

If nothing else, at least it works until some purist or local can make it more accurate and pretty on later a later date. :stuck_out_tongue: