Aerial Imagery for OpenStreetMap


Anyone can contribute to OpenStreetMap, and there’s several complementary techniques for mapping. One of them is to use aerial or satellite imagery that has been cleared for use as reference material for OpenStreetMap. Yahoo! was the first company to grant such a license on their worldwide imagery to OpenStreetMap. More recently, OpenStreetMappers have been able to trace over Bing aerial and satellite imagery, which meant an increase in resolution and coverage for most regions in the world.

Editing OpenStreetMap with the help of Bing imagery

There have also been special cases where companies have provided imagery resources for smaller geographical areas, as was the case after the Haiti earthquake. Many national, regional and local governments have aerial imagery available as well, and some have provided their imagery to OpenStreetMap for mapping purposes (here‘s an overview).

Why are local OpenStreetMap groups and individuals engaging with their governments to gain access to aerial imagery when OpenStreetMap already has Bing as a great, worldwide resource? There are many. Bing does not cover the whole world in high resolution imagery, which is needed to map roads, buildings, sports facilities and most other features you see on the map. Where high resolution imagery is not available from Bing, local resources may be able to fill the gap.

Another reason for wanting to use local aerial imagery is currency. Bing imagery can be years old – the age of the imagery varies greatly. Without local knowledge it can be hard to establish what the age of the Bing imagery for your region is, although this tool can help. If the Bing imagery is more than a few years old for the region you want to map, you will not be able to derive the latest changes – new roads, a new residential area, a torn down baseball stadium – from that imagery. Mappers who are unaware of the age of the imagery may put in features that are no longer there, or destroy more current information thinking they are actually ‘improving’ the map!

So even though Bing is a great resource for OpenStreetMap, access to local aerial imagery may help improve OpenStreetMap a lot! So if you’re an OpenStreetMap contributor, check with your local government’s GIS department and see what they have. They may be willing to grant OpenStreetMap access to it. If you represent a local, regional or national government and have imagery available, contact a local OpenStreetMap group (or me if you can’t find one) and see how you can help make the free and open world map even better!

Utah

I got in touch with the GIS department of the state of Utah right after I moved here, and it turns out they have some great resources. They have 1m imagery from 2011 covering the entire state and 25cm imagery from 2009 covering the major urban areas. You can see the importance of current imagery in this side-by-side comparison of Bing imagery (top) and the state imagery (bottom):

How to add an imagery layer to JOSM

The screenshots are taken right from the advanced OpenStreetMap editor JOSM. It’s really quite straightforward to add a new background image resource to JOSM, provided it’s available as either a WMS service or preferably a tiled map service following the TMS protocol. To add an image resource, go to Edit > Preferences… (F12) and click on the imagery tab (the green one that says WMS TMS). The top part represents all the imagery layers that are built into JOSM by default. The bottom part represents the active layers, and you can add your own there by clicking the grey + next to the list. A smaller window pops up; this is where you add the imagery layer details: its name (you can make that up) and the base URL of the WMS or TMS service.

For WMS, that’s the URL of the service without any of the WMS parameters. Clicking ‘Get Layers’ will retrieve the available layers from the service and present them. All you need to do is select the layer you want to add and press OK. The layer should now appear in the Imagery menu of JOSM. In the case of the Utah imagery, the URL is

http://mapserv.utah.gov/ArcGIS/services/UtahBaseMap-Imagery2009/MapServer/WMSServer

For TMS, the process is a little different: you need to figure out which parts of the TMS URL represent the zoom level and the x and y location of the image tile in the URL, and insert them as {zoom}, {x} and {y}. Look at the default layers if you get confused. The provider of the service will also be able to help you figure it out!

Don’t forget to always get permission from the service provider first! The fact that the service is publicly available does not mean that it’s OK to use it for mapping in OpenStreetMap! Discuss with the provider of the imagery, and if in doubt, get in touch with the community through the legal-talk mailing list or IRC. And don’t forget to document the imagery on the wiki: edit the relevant page for your region, town or country, and add the resource to the Imagery Overview page.

3 thoughts on “Aerial Imagery for OpenStreetMap

  1. I’m fairly new with OpenScales. For what you say in this article, I understand that OpenScales users can legally use Bing Maps. Is that so?. Is that also true of geocoding functions or is this applicable only to imagery?. Is there a particular url resource I should use?

    Thanks

    • If you mean OpenStreetMap (I do not know what OpenScales is) – the license only applies to the use of satellite and aerial imagery as a backdrop in editor software, so as to support improving the data in OpenStreetMap. No geocoding, rev geocoding, or other Bing Maps functionality was licensed to OSM. See here for more info and to review the full license text: http://wiki.openstreetmap.org/wiki/Bing

  2. Hey Martijn! Thanks for posting this article! im really impressed by the quality of this aerial image. Thanks also for the tips you gave. I couldn’t agree more that some of us seeks for a better resolution of image that’s why many are engaging to create a better quality of aerial mapping. Is the software you used can also perform a 3-dimensional image too? Thanks for the response, cheers!

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