Add capability to see raster map layers underneath our vector data

[jeffreyameyer]

What's your idea for a cool feature that would help you use OHM better. Ideally, visitors could compare the vector data on our map to an underlying raster of an old map. This would provide a richer interactive experience, by allowing visitors to see both the old maps, as well as relevant vector information.

It would be something like this, from imaginerio:

although I would probably put all (or much more) of the vector information and not just the points on top of the map, so the map viewing experience would be a bit like the visual editing experience, but not limited to high zoom levels. Something like this, from JOSM:

A cool example (that I don't have yet!) would be to show information relevant to the bbox and time of a map, but that wasn't included on a map. Obvious examples would be indigenous people's presence showing on top of an old fur trapper's map.

An MVP would include:

• URL-based method for adding a map underneath the vector data from an xyz source (to start)
• A UI-based method for adding 1 map URL

Current workarounds Is there any way to meet this need using a workaround or "hack" right now? Third party sites and hacked up demos.

Additional info Split out from #525

[1ec5]

It sounds like the use case is to make an old map interactive. This is a completely different use case than the existing main map, which focuses on exploring OHM data. It’s a totally valid use case, but I wonder if we’d be better served by standing up a separate tool, based on existing georeferenced image viewers, that can additionally “annotate” the image based on OHM data. This would keep us from having to figure out how to shoehorn even more custom functionality onto the homepage. We already struggle to ensure sufficient contrast on our styles as it is, without putting arbitrary imagery behind it.

[jeffreyameyer]

Three thoughts: 1) The primary, mvp use case is for observation and to put the vector information into context. Interaction is not necessary. 2) You're absolutely correct that, in spite of (1), this may be pushing toward a different site for additional levels of interaction. My hope was that we could get to (1) without a lot of extra work. If we were to have a different site, we'd need some very direct paths to get people from that site to the editor on OHM. 🤔 3) Good point about the styles - clearly, we'd need a different style to highlight the info that was to be presented on top of the old map, something like in iD or similar in effect, but not in execution, to the garish red roads above.

Example of (3), from iD:

[1ec5]

How do people normally read a mashup between an old map and a vector layer such as the one mocked up above? If, in the best case scenario, we’ve mapped everything that’s on the map and more, does the map become nothing more than a rustic paper texture? Or does the reader expect the vector layer to highlight only the most important information on the map according to some criteria?

[jeffreyameyer]

This is a great line of questions and figuring out the answers will help us show if there is - and I believe there is, but I could be wrong - a value proposition for the masses of historical vector maps vs. just looking at old maps.

First, I don't think there's any "normal" way to read a mashup between an old map and the vectors extracted from it or superimposed on top of it.

At a minimum, I think it will be a guide for people trying to extract information to look at an old map and see what needs to be mapped. Or, it could help enhance old maps by tying them to known features (this feature is on this map) or for finding other maps that contain whatever the vector features are. There are other ways this might work as well... imagine an invisible line with just labels for roads, a kind of locator layer for the old maps.

But... those examples aside, I think it reduces the burden of people looking at limited subsets (avoiding the completely mapped scenario) of mapped data for imagining the context of what is missing.

I also don't think people are used to being shown what's not on a map. So, viewers could see what other information was not put on the map. Sort of an x-ray viewer.

The most important reason to show both raster and vector info together? People just like the texture of old maps. They are art. They give texture and a human touch to the approximated, crooked lines of digital vectors. Hand-drawn, smudgy lines > crisp, machine-drawn lines.

And, in the case where everything on an old map has been extracted and rendered in OHM, the map rendering will never be just an old relic; it will be (some degree) of proof for the vector data shown on the map and hopefully give users confidence that the vector data isn't purely made up bs!

As for the highlighting of what's important, I think that would / should be separate from OHM directly, unless we decide to enable some sort of curation feature, but that's probably in the client's hands.

[1ec5]

And, in the case where everything on an old map has been extracted and rendered in OHM, the map rendering will never be just an old relic; it will be (some degree) of proof for the vector data shown on the map and hopefully give users confidence that the vector data isn't purely made up bs!

I think this is a great insight. Even when it comes to paper maps, the publisher asks the reader to trust the map contents to some extent. As an open data project, we value transparency; showing our sources inline would seem to align with that value.

Still, I think there’s reason to be cautious. Replace “old map” with “aerial imagery” and you have a case for showing a satellite or aerial imagery layer beneath OpenStreetMap on osm.org. There have been many calls to do that over the years, but it got caught in tension over whether to optimize the site for end users, inviting unflattering comparisons to Google Maps. Procuring worldwide aerial imagery would be challenging, since vendors like Bing and Esri only license their imagery for use while editing.

Even if OSM could overcome these logistical problems, there’s been concern that it would distract the community from the core task of mapping and confuse newcomers about the project’s purpose. Why doesn’t it show traffic congestion on the map too? One common sentiment is that the site shouldn’t even have a prominent, usable map on it and should instead focus on providing information about data reuse and community events.

There are parallels to that perennial debate. With an old map layer, we may invite unflattering comparisons to sites that focus solely on viewing old maps rather than singing to our strengths as a repository of new data about the past. The comparison would be unflattering because other sites have a head start in curating old maps, and because our user experience is strongly tied to map creation.

For our project, a mission of mapping the world throughout time has a certain clarity that might be undermined by introducing features that appear to curate old maps. I have encountered many people who are disinterested in OHM and don’t think they have the chops for it, just because they assume that we limit ourselves to curating and annotating old maps. Yet there’s so much more to documenting historical geography! How can we nod to this important method without allowing it to dominate the conversation?

[jeffreyameyer]

Still, I think there’s reason to be cautious.

No doubt. This should be thought through carefully.

Replace “old map” with “aerial imagery” and you have a case for showing a satellite or aerial imagery layer beneath OpenStreetMap on osm.org. There have been many calls to do that over the years, but it got caught in tension over whether to optimize the site for end users, inviting unflattering comparisons to Google Maps. Procuring worldwide aerial imagery would be challenging, since vendors like Bing and Esri only license their imagery for use while editing.

I'm less concerned about unflattering comparisons, as that's all we might have right now. Also, I don't think we should be compelled to have worldwide coverage of aerials. But, where they are available, it would be an interesting complement to our data. Again, nothing beats ground truth for representation of what's there.

I do think the question of who are the end users we're optimizing for is one we should consider always. Is this to help editors? What does that mean? Same for casual viewers. I think one of our key differences with OSM here is that we may have a heavier weighting of the casual viewer than OSM does. And, as always, perhaps that casual viewer site is a separate or adjacent site that we build.

The comparison would be unflattering because other sites have a head start in curating old maps, and because our user experience is strongly tied to map creation.

Good point, however, I'm hoping we could mitigate this with a strong partner value proposition with libraries (IIIF) or online sites / hosts of georeferenced maps (libraries, Old Maps Online, Wikimedia, etc.)

Yet there’s so much more to documenting historical geography! How can we nod to this important method without allowing it to dominate the conversation?

Truth! This should be addressed. Perhaps through documentation, site language, UX controls, and ideally, incorporation of other non-map-based georeferenced information - newspaper articles, business directories, photographs? Who knows, maybe a combination or even none of the above. Just needs to be thought through in a way that encourages continued historical mapping that we know, instead of discouraging it.

[jeffreyameyer]

Here's an example of where it might be pretty cool to be able to underlay a raster. It's from an ESRI Story Map about the Tennessee sites listed in the Green Book travel guides.

In this case, the contextual historical map (a high contrast b&w Sanborn?) is just that... a static image. A user is expected to connect the primary map pane to a non-georeferenced picture of the same area. That's a lot of mental gymnastics and seems to take away from, instead of adding to, the context of the story. For me, I'd like to see what other businesses surrounded that Green Book business.