I'm speaking from the perspective of greybeard-advising and helping with an import of building footprints from MassGIS, in which Jason Remillard did almost all of the prep work, and multiple people (basically all the active mappers in Mass who answered our messages) helped with checking the proposed upload files. Please note that I am generally on the pro-import side of things, so even though I have a lot of pointed questions I'm not trying to discourage you -- just to point out where there is work to do in defining the proposal to the point where this group could address it. I am also not speaking from any particular position of authority, merely as an imports list member and one of the active mappers in Mass (who knows most of the other active mappers by email and some in person, at least the non-reclusive ones).
It's great that your county is willing to make data available under a compatible license. Even if you don't continue down the import path, openly publishing data under a clear license is a huge step, because it enables anyone in OSM to begin thinking about imports, or examining individual details. Imports should be done by experienced mappers. Are the people who will be doing this already mappers, who have learned JOSM and done significant mapping (at least 100 changesets over several months)? (The mass building import group had several thousand changesets and over 10 years of editing spread over a half dozen people; that felt about right to be doing an import.) This is particularly important since in OSM there is no simple replacing of layers with a better dataset for that layer, and this becomes far clearer after working with editors for a while. Imports are required to have community support. Do you know who the active mappers are in your county or state? Have you met/emailed with them? What is their opinion of this? Are they willing to help with QA? You are proposing a very large scale import (really 5 of them), some of which (roads, buildings) have very significant issues with conflation of existing data. Park boundaries and trails are probably less difficult, because I'm guessing 100% human review is possible, and hydrology may or may not be tricky depending on how much there is. Still, there is a strong norm about not overwriting hand mapping with imported data, and the import workflow will have to be organized around respecting that norm. You will likely have to set up 5 wiki pages to describe the 5 imports. The first issue is licensing. Just 'publically available' is not enough; you will have to have the agency state that the date is public domain or have an explicit license that meets the contributor terms. In addition to the original data being available, you should prepare to publish the source code of how you translate that data to osm files, and how you prepare change sets that would be uploaded. That might be a program that loads OSM data into postgis, loads the county data, and produces change files. Part of this code is explaining how all the (presumably) attributes in shapefiles are turned into osm tags (or omitted, like county unique identifiers). You should also think about how/if future updated county datasets would be handled -- is there some notion of incremental updates? (In Mass, we had these change files (add only, actually) broken up by town, as this is how the source data was. The basic plan was to take each building polygon from MassGIS and to put it in the output file only if it did not overlap any building in OSM. That resulted in some non-imported buildings, but did not overwrite any hand-drawn work. In the end, we found that all was well with this import, except that a few tents were added as buildings which we clean up as we notice, probably under a dozen out of 2E6 buildings imported.) For buildings, you could use a similar approach to what we did in Mass. You could also output some other kind of difference file for buildings that do overlap, to understand what's different, and perhaps set that up for some sort of maproulette challenge, but that's harder and I'd put it off to a second round. Here are some pointers/examples and code, which could be reused significantly if not entirely: https://wiki.openstreetmap.org/wiki/MassGIS_Buildings_Import https://github.com/jremillard/osm_building_import Note that the import guidelines and demand for rigor have strengthened since then, so while what we did is still ok, you may have to make a clearer explanation of choices and consequences. For roads, surely you will find that tiger roads are already there. For roads not touched since the tiger import, a way to adjust geometry and attributes from the better data sounds conceptually reasonable. However, this is easier said than done (especially not breaking connectivity at roads that cannot be updated), and you will definitely have to publish the code so that others can run it and look at the proposed changes. This is almost certainly the hardest thing of the list you propose. Buildings may be the best thing to start with, as adding high-quality non-overlapping buildings raises the fewest issues. Trails data might well be integrated incrementally by existing mappers, once published, also, depending on how much there is. Probably it's big; just my single town has over 100 trails, so the county is probably at 5K. I can't emphasize enough that publishing the data with a clear license is the first step, and that enables others to help. I suspect that a number of imports@ people don't really want to put time into helping until that's done and the license is known to be ok and the data can be looked at by some others. Greg (osm user gdt)
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