Why can't two connected street segments have an identical range number at the connec?

675
2
11-01-2013 10:56 AM
ElizabethWindsor
New Contributor
This has bothered me ever since I was first trained to range street segments.  When segment A's TO node connects to segment B's From node, and they comprise the same street, why is it that the last number of segment A's address numbers range mustn't be the same as the first number of segment B's range? It seems to me that the two nodes identify the same point on the ground and that if I use two different address numbers at the connecting ends of the segments I'm losing however many feet are supposed to be between those two numbers, thus skewing the accuracy of the geocoding of the addresses on one or both of the segments.  Was I taught incorrectly?  Should I have been using the same number all this time?
Tags (2)
0 Kudos
2 Replies
TimWitt
Frequent Contributor
Elizabeth,

The problem is that if the 2 street segments have the same number (one is FROM and the other would be TO), there would be 2 results when looking for this address, which is not possible. Some 911 mapping software struggles with this and might delay a response, when the dispatcher has to choose first which one is the right location (even though technically both are the right location) and then it locates the address.

So when a call comes in and you don't have the issue stated below, the mapping software can immediately zoom to the address since there is only one address to choose from.

I hope this makes sense!

Tim
0 Kudos
JoeBorgione
MVP Esteemed Contributor
+1 to Tims comments; the two CAD systems I work with will choke on over lapping ranges.  They also prefer continuous ranges along streets of the same name.

As far as accuracy and or precision when geocoding against streets, the best you can hope for is to be accurate.  If you have a range of addresses on a street that go from 100 to 200, you'll geocode house # 150 on the even side of the street in the middle of the block.  Thats pretty good accuracy.  However, what if house # 150 is actually located on the odd side of the street, and is the last house (at 2nd Ave; 200)?  No real precision there.

Geocoding against a linear feature is at best an interpolation function of range and segment length.  If you adjust your ranges one digit either way, that may affect the block that address lands on.  However, you're never going to achieve a precise 'hit'. 

I'm not a fan of address ranging street segments based on actual physical addresses.  If you want/need that sort of precision, get yourself some good point data.

What's especially important in 9-1-1 address ranges is to include the intersections.  Obviuosly there is no structure in an intersection, but in our business, a lot of bad things happen in them:  lets say you have a street calle Elizabeth ST and it starts at 1st ave, crosses 2nd Ave and 3rd Ave then terminates at 4th Ave.  Assuming the local grid values of the avenues are 100 based, the three segments of Elizabeth St should look like this:

100-198  (Low range covers the intersection Elizabeth and 1st ave)
101-199

200-298  (Low range covers the intersection Elizabeth and 2nd ave)
201-299

300-400  ( Low range covers Elizabeth and 3rd AVE and the High range covers Elizabeth & 4th Ave)
301-399

One might argue, " Well, I'll just use the intersection function like &,|,@"  etc.  Sure, but in 9-1-1 typically your CAD needs to assign an address to the interesection in the form of HOUSE-NUMBER, STREET-NAME (like 400 Elizabeth St), so you may as well keep it tidy.
That should just about do it....
0 Kudos