[Talk-ca] Address ranges

[Steve Singer]

I'm starting to think about how we might want to import address range data 
from Geobase/Statscan into OSM.

The Karlsruhe schema
http://wiki.openstreetmap.org/wiki/Proposed_features/House_numbers/Karlsruhe_Schema 
seems to be the most popular OSM method of adding address data.

It uses a node (that is not part of the road) that is placed at the location 
of the house/building that address information is known about.  These nodes 
are then connected with interpolation ways.

The GeoBase address data (and the StatsCan data) give block face addresses. 
The datasets essentially say for this block(road segment) the first house is 
100 and the last house is 120; along with some interpolation data.  We don't 
get the coordinates of any houses/addresses on the street.

Consider these example

Say we have two streets, Main Street (--) and First Street (***) made up of 
4 road segments.

                     *(3)
                     * 
--(1)--Main Street--+---(2)-
                     *
                     *
                     *(4)


The block face based data we get might tell us that road segment (1) is 
100,150 on the right side, 101 to 102 on the left side

Segment (2) is 152 to 160

Segment (3) is 10 first street to 14 first street

and segment (4) is 16 first street to 20.

If we wanted to translate this to the Karlsruhe schema we could create nodes 
at the start and end of each road segment(based on the geometry coordinates 
of the road from the NRN/stats can data).

These leads to the following issues:
1. Do we create the address nodes on the street, in which case they would 
occupy the exact same coordinates of the nodes that make up the road itself? 
Or do we try to offset the address nodes to the left/right of the roads by 
some artificial amount (say 3 meters).

2. The point on my diagram marked (+) is an intersection of 4 road segments. 
Our block face data gives us 4 addresses at that single point(8 if you 
count both sides of the road).  This isn't a problem if we are coming up 
with offsets.


When we import address data I am thinking that we would import it for all 
roads, not just ones the ones that came from geobase.  Since address 
nodes/ways don't' get connected to the roads anyway I don't see the harm in 
adding address for pre-existing roads or ones that the import skipped. 
There will be some positional consistency issues but we are going to have 
those anyway if we are offsetting the nodes by some arbitrary amount.

In cases where we are able to attach the road(way) in OSM with the address 
then we can create an optional relation linking them.

If anyone is aware of another data import that used a block based address 
source (versus a data source that has an entry for each lot on the street) 
I'd appreciate a pointer to it.

Thoughts?


Steve