How can I resolve the conflict? Do I move the building outline? Do I plot the footpath along the satellite image and ignore the violation? Any other suggestions? The specific location is OpenStreetMap (Chelsea North Elementary School)
If I extend the footpath to the East along the satellite image, it passes through the building outline. I can use the Imagery Offset to move the image relative to the building outline, but the footpath is attached to the building outline location. The actual footpath extends to the East (right in the image) to the intersecting North/South footpath paralleling McKinley St. But extending the existing footpath flags the building/footpath violation.
Hello Donald, and welcome. 
If youāre confident that the building footprint is out of alignment, you can feel free to move it. Itās not uncommon for building outlines traced from satellite imagery to appear a bit off because the aerial imagery isnāt perfectly centered above the building, and hence the building will appear skewed on the image. Ideally the outline as it appears in OSM should be adjusted to be where the walls meet the ground.
At first blush it appears the school building outline is out of alignment with the rest of the things on the map. For example the McKinley Road line object to the east looks to be aligned with the centreline of the roadway. The school building appears to be about 3 m north and 2.25 m east of where it ought to be.
Using the iD editor, you can select the building area and type āMā on your keyboard to move it. Something like this looks about right:
2 Likes
Thank you very much. That was my inclination, but Iām new and donāt want to muddle the good work that has gone into all the maps!
Just to clarify: you are not likely to have parallax issues with actual satellite imagery just with aerial imagery. Besides that the imagery can naturally simply be offset for any number of reasons, though most sources we have access to these days are far better in that respect as they used to be.
Hello.
In future, may I suggest a solution which will be quicker and easier for you, and which makes the Map clearer and easier to read?
Instead of (laboriously) drawing the footpaths along the road (on both sides in many cases!), taking care to create crossings/ intersections for all the road junctions/ driveways/ service roads, and naming the footpaths with the name of the road so that routing engines can provide the information to the pedestrian, mark the road itself with sidewalk=* (left/ right/ both/ none).
Particularly in busier environments - where you or another Cartographer might wish to add trees, bollards, post boxes, service roads, street cabinets, bins ā¦ - life is also easier with sidewalk =* , because there wonāt be the need for later Cartographers to āfaffā with the existing features to insert the desired elements. They will quietly thank you.
Of course, I am aware of the pros and cons table on the Sidewalks page of the Wiki; I donāt agree with the points in āPrecise coordinatesā for the reasons Hoserab elaborates (pace, SimonPoole). I see the assertion that āseparate ways predominate in North Americaā, but that in itself isnāt a deciding factor, although I can understand the temptation where there is a strip of grass between the footpath and the roadway.
Another benefit of sidewalk=* is that when separate footpaths stop, as in the image here, the Cartographer is saying that there is no further footway route. Remember that the user and the routing engine donāt also see the aerial image. Consequently, the diligent Cartographer must continue with more and more footpaths, cluttering the Map, when the time could be spent more easily, more enjoyably, and more productively attending to other features.
1 Like
Upon further consideration, though moving the building outline worked in this case, is it generally the case that the aerial imagery can be considered authoritative? Should I have validated the accuracy of the imageās location with [some independent] source?
No.
As I said the imagery available to us is a lot better than it used to be (the original Bing release had bits that were more than 50m offset not far from where Iām sitting right now), so it is less of an issue, but checking against other sources and if it is only a bundle of GPX tracks is a good idea.
2 Likes
Since I walk that path regularly, Iāll capture some tracks and check alignments. Thanks to all again.
1 Like