[Imports] Tanzania buildings

[Mikel Maron]

Hi Msilikale, Rob

Msilikale, thanks for the initiative of sharing the Dar building footprint data set (which btw is posted at https://www.dropbox.com/sh/oe08t8tirw7qtuk/AiOhiUBEN5). It is certainly comprehensively covering the whole metro region, and beyond, massive! Actually, can you explain the boundary of data set? Seems like the urban expanse to the south is suddenly cut.

I took a look at this data set, compared to what's presently in OpenStreetMap. Certainly much greater coverage in the government data set. But many of the buildings in OSM have other valuable tags. Any import process would want to retain these.

Additionally, there appears to be a consistent offset in this data set. I'm not sure if it's an artifact of the reprojection, or in some misalignment in the georeferencing of the source imagery for this building data set (I assume it was digitized from imagery); or if there is misalingment in Bing imagery in Dar (though I suspect not, both Google and Bing align decently well).

Looking at the geometries of the building footprints themselves, some look decently accurate relative to the imagery, but in a great majority of cases there is not correspondence, in a number of ways. Sometimes an individual building is broken up into several. Other times, the footprint is partially correct, but then in other parts wrong. And in other cases, there's clearly been new construction. This is mostly looking in the Central District. If I look at some place like Tandale, there seems to be even less correspondence (to be fair, OSM is not much better here).

If this data were to be imported, it would need to be looked at very carefully, piece by piece. It couldn't be done in bulk I think. Could be a big detailed job. And I wonder, would it end up being more work to try to get this data set to fit the existing OSM data, and imagery, than simply organizing to trace buildings directly from imagery. Could even possibly be an interesting microtasking exercise, ala http://buildinginspector.nypl.org/

In any case, Msilikale, worth reading through the Import guidelines to lay out some of the other considerations, and good next steps, like documenting this data set and deliberation in the wiki. http://wiki.openstreetmap.org/wiki/Import/Guidelines
 
Best
Mikel

* Mikel Maron * +14152835207 @mikel s:mikelmaron

On Monday, April 21, 2014 5:45 PM, Rob Nickerson <rob.j.nickerson at gmail.com> wrote:
 
Hi Msilikale,
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>Thanks for uploading the Tanzania, Dar es salaam buildings data to dropbox. I've downloaded it and had a quick look. The tags look like they are not needed with the only one that *may* be useful being called "BIN" - I have no idea what it is. Do you know?
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>I will split the file into smaller sections for you and give you a link to the download. Please give me a few days. I will aim to get it done by the end on next weekend. If not then feel free to contact me to remind me.
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>Rob
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