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I'm a beginner to OSM and have started off by mapping local waterways for recreational use. I've noticed several popular lakes & rivers in my area which are not yet mapped, and yet the surrounding land areas have already been mapped with great detail. Could it be that mappers are waiting for winter imagery so that shorelines are not blocked by trees and can thus produce more accurate results? I would like my mapping to be as accurate as possible, but am I overdoing it? And do the various sources change their aerial imagery seasonally?

asked 26 Jul '12, 14:52

riverpaddler's gravatar image

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I don't know about other regions, but the area where I am mapping has bing-imagery that is 2 years old.

It is of course great, that you want to map as accurate as possible (everyone should do it), but better is it to map a missing feature now, not in the best accuracy, and fix it later, if better sources are available. It is at least preferred to not mapping a feature at all, just because some better source might be available in a year or two...

(26 Jul '12, 16:27) moszkva ter

Could it be that mappers are waiting for winter imagery so that shorelines are not blocked by trees and can thus produce more accurate results?

Likely, no. When I first started mapping, few of the nearby lakes and rivers weren't mapped, but it was because no one else had simply mapped them yet.

And do the various sources change their aerial imagery seasonally?

Usually, no. The aerial imagery is not created by OSM and is created by several different companies. OSM just has permission to use it. The imagery is updated at random times and we cannot request the company to update it. without regard to the season. See the FAQ For more information.

One of my mantras (and I think it's shared by many other mappers), every little bit of mapping information and features helps, even if it's not the best or extremely accurate. It can be improved upon later.

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answered 26 Jul '12, 18:19

skorasaurus's gravatar image

accept rate: 12%

edited 31 Jul '12, 07:44

scai's gravatar image

scai ♦


I suspect that images are made with a high summer sun (I am talking GB here) to reduce shadows and get best images. I can't remember seeing a live tree in the images without leaves, suggesting summer of course. I find that as you will see the bare bank line here and there you can judge the over hang of trees. I think that good guess banks lines are better than no banks at all. But it all depends on the area having good image quality. We are lucky to have Bing as without it and without being able to access the bank on foot lots of water mapping was down to very primitive survey methods.

(26 Jul '12, 20:53) andy mackey

Regarding when imagery is taken, it depends on who's collecting the imagery. Lots of the (non-commercial) high quality imagery in the U.S. is funded by the Farm Services Administration, so that's usually done "leaf off" in the spring.

(27 Jul '12, 14:39) neuhausr

Essentially, people map what they're interested in. That might be geographically based, or it might be for a particular purpose, or perhaps just railway infrastructure, or perhaps cycle routes. Perhaps near you everyone's concentrating on roads and hasn't got to other features yet? If so, it sounds like you're the perfect person to do the waterways!

As has already been said, aerial imagery most usually doesn't update more than once a year, so you may have a long wait for your "no leaves" picture.

One thing that you might need to be a little careful about is that the imagery that you're using isn't offset with respect to other sources. Things that might tell you whether it's offset or not include GPS traces that have already been uploaded (the more traces, the better), other imagery sources, and other imported data, if you're happy that the source of the imported data is accurate enough. If you're unsure, you could post a link to the area that you're interested in here and we could take a look.

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answered 30 Jul '12, 15:16

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SomeoneElse ♦
accept rate: 16%

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question asked: 26 Jul '12, 14:52

question was seen: 4,301 times

last updated: 31 Jul '12, 07:44

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