[OSM-talk] TIGER 101

[Ben Gimpert]

Hi Schuyler,

If you take a look at the Tiger.import method in:

	http://svn.openstreetmap.org/utils/tiger_import/tiger/tiger.rb

...you'll see what I mean.  In my English:

Regardless of what it says on the tin, the actual latitude and longitude
"numbers" in the TIGER dataset are *not* generalized into the concept of
a "node" or "point" or "road intersection" or whatever.  Each line in a
FIPS county's .RT1 file is a "street" (roughly).  Each contains starting
and ending latitude and longitude points, expressed as raw coordinates,
not as "node ID's."  In that same FIPS' .RT2 file, there are a secondary
streets -- defined again as a sequence of raw latitude and longitude
points -- that can be merged into the .RT1 primary streets.

The important thing to note is that there is *no* level of indirection /
abstraction / generalization / whatever for nodes.  Everything is a raw
latitude and longitude number.  I hope this makes sense, because I think
the folks on this list might be overestimating the quality and
generality of the TIGER data.

		Ben


On Thu, 30 Nov 06 @09:41am, Schuyler Erle wrote:
> * On 30-Nov-2006 at  8:37AM PST, Ben Gimpert said:
> > Hi Andy & Steve,
> > 
> > Right, nodes are not being reused.  This is just because of how they are
> > represrented they are represented in the TIGER data itself.  I've posted
> > about this before -- how "5th Avenue" in Manhattan is actually N
> > separate record chains in TIGER, though obviously it's a
> > physically-contiguously street.  And that this occurs also at the node
> > level, where there is no level of abstraction in the TIGER dataset for
> > shared nodes.
> 
> Could you explain this in more detail? The "T" in TIGER stands for
> "topological", so it ought to be possible and even easy to reuse
> nodes, unless I misunderstand what you mean by that.
> 
> SDE
> 
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