[Talk-us] Discardable TIGER tags
phil_g at pobox.com
Mon Jul 30 13:09:08 BST 2012
* Alan Mintz <Alan_Mintz+OSM at Earthlink.Net> [2012-07-29 18:54 -0700]:
>  When combining ways in JOSM (at least), values for tiger:* tags
> are combined with ":" (colon) as a delimiter, instead of ";"
> (semi-colon). Why, and should this be changed?
I believe this behavior was intended to make tiger:tlid merging work a
little better. As I understand it, the TIGER data originally imported was
structured so that a single road was composed of many segments connected
end-to-end. For the import, all segments with the same data values were
concatenated into a single way and the IDs of each constituent segment
were concatenated, separated by colons, and stored in the tiger:tlid tag.
Thus, when combining two TIGER ways, using a colon to join their
tiger:tlid tags would give a roughly correct reflection of the mapping
between TIGER data and OSM data. I don't know why the decision was made
to apply that to all tiger: namespace tags rather than just the tiger:tlid
Obviously, this doesn't help with way splits; the tiger:tlid value gets
copied to each half, even though the original segments are now divided
across the two ways. On top of that, TIGER doesn't use the segment
structuring anymore; their data is more like OSM now, and each road gets a
feature ID that's unrelated to the old TLIDs (though there might be a
table somewhere providing a correlation between the two systems). Given
all that, it seems reasonable to drop tiger:tlid on edits like the
 Plus my personal experience that I periodically have to delete
tiger:tlid tags after merging ways because the resulting tag value
exceeds OSM's length limit.
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