Thanks so much for your elaborate reply and a bit of additional explanation. It seems logical to me, for a platform akin to OSM, that the objective is some kind of synthetic reconstructive representation of historical empirical reality. This does mean that it becomes absolutely crucial for it’s usability that any edit (and potentially multiple versions or readings of a single area or detail) are traceable to source material. Otherwise it would become very difficult to place nay trust in that synthesis later on as a truly critical resource. I have spent very little time exploring, but I dont know how sources are treated and tracked currently. I did notice the difficulty about permission to use material for vectorisation. I’m a little confused as to what this issue extends to, since I’d think that one is free to vectorise whatever is feasible, but not free to the also publish the source material. I’m not an expert on such issues of rights, but it could become hairy pretty quickly. I also don’t think that all archives would properly expect this use of their material.

Regarding de facto and de jure boundaries, I note you’ve opted for very explicitly legal terms. I’ve published on boundaries and used the philosophical concepts of fiat and Bina fide boundaries (of objects or spatial entities, derived from Smith & Varzi) in mapping. For representations of information on maps I continue to find this very useful.

The example you gave of California as an island is interesting. Of course, it becomes very tricky to figure out which actual geographical knowledge could be contained in a document which depicts an entire region as an island we factually know not to be. Nonetheless, it would also be a real pity, historically speaking, if this would render such historical mapping sources essentially unusable. Personally, I feel that it is important to have vectorisations consultable next to geolocated and rectified raster maps for research purposes. In addition there could even be entirely reconstructive vectorisations, which then require marking up as interpretive reconstructions, placing a lot of emphasis on metadata and the process of making. Since I’m carrying out a postdoc project which also touches on all of this (though not a completely conjured up geographical reality, like the California example) I’m still not entirely decided on how best to do this. Part of my interest in OHM was also to find out if it could be the right platform to potentially ‘release/disclose’ (some) of my research data. I’m not clear on that either so far. Possibly because the project wouldn’t respect the parameters set for OHM only an adjusted format of the vector data could become part of OHM alongside other ways of presenting and offering the data.

Good to know I missed something on the time slider. The daring requirement of features, while entirely logical and necessary, is also a tricky one. Very often the precise start and duration of any feature (not even entire spatial objects) is unknown, and historically speaking it would be very useful to have the source that claims the appearance, alteration, or destruction/removal of spatial entities. This becomes even more finely grained when it is the uses that change, not the physical (or legal-spatial) entity.

Very nice! In my opinion there is definitely value in retaining as much information as possible from historical sources when ‘digitising’ them. Though this brings into view a discussion about whether one is mapping a best proven version of a previous physical state of development of a landscape or whether one is converting historical sources in a different format to enable alternative (linked) uses. I think any historical GIS ideally would enable both. Or, that is to say, retain traceability of information to the historical source and marking up what of that source is interpreted to be a reflection of a previously existing empirical geographical state or a (historical) construct.

It is not unusual for planned or proposed urban developments to make it onto ‘official’ mapping sources. There is plenty of evidence of historical maps copying information from previously existing maps too (one presumes without putting much effort into checking them). Naturally this also brings into consideration the purposes the maps involved were intended to serve. Explicit navigation doesn’t seem very likely in these instances! The Sanborn maps are (once again) revealed to be valuable and reliable sources, as they clearly recognise the nature of the geographciallly projected situation. Nonetheless, there is an interesting question about the history of the proposed streets and how this is treated administratively and why it never became relevant to update to an empirical reflection of the situation in any of these maps. Indeed, as well, why this proposal still seems to hold relevance presently. What is the legal/land registration status of this?

(Disclaimer: I literally just joined this platform out of curiosity, but am not aware about its explicit purposes or how these are defined. It could well be that the aim is not to digitise all and specific historical sources, but to come to an as reliable as possible interpretation of empirical geographic states of development as we can collective prove to have existed for any point in time. Why, by the way, is the timeline limited to 1825?)