[Talk-us] US Addressing

[Brian May]

On 11/29/2012 10:45 PM, Mike N wrote:
> On 11/29/2012 10:32 PM, Paul Johnson wrote:
>> Is there a compelling reason not to get parcels instead?  As parcels
>> change shape, the centroid can be easily interpolated.  It's not really
>> possible to extrapolate geometry from centroid, however.
>
>  It would be useful to navigate to address points - properly placed, 
> they will lead to the building of interest or driveway. Centroids on 
> large parcels will frequently misdirect to a side street with no access.
>
Right. From what I have seen, an address point layer is "rooftop" 
points. In the example of Lake County, they centered the points on top 
of residential structures, and for retail commercial, they put the 
points at the store fronts. There may be some variations, as Richard 
pointed out, for rural areas they may put the points at the ends of 
driveways. In Lake County, they put the points on the residential 
structure on large parcels. You can check out the Lake County data by 
looking at the Address Locations layer in the online map viewer: 
http://gis.lakecountyfl.gov/gisweb/

Parcel centroids are a fall-back position if the address points are not 
available. Parcel centroids do work really well for smaller residential 
lots. For large parcels, you can generate centroids that fall within the 
parcel (even for irregularly shaped parcels), but still need to properly 
place the points, And then for condos and multi-tenant commercial, you 
need more points than is in one parcel. For condos, sometimes the 
appraiser maps "fake" polygons for each condo, and you can use those as 
a starting point. In other cases, appraisers stack the parcel polygons 
on top of each other to represent condos. In other cases, they map 
building footprints and split them up by the number of condos in the 
building. And the list goes on...

Brian