Determining if Parcel is Sub-Dividable?

Question

I am trying to determine which residential real estate parcels are sub-dividable but am running into issues when it comes to placement of an already existing structure on a parcel.

For example, let's assume the minimum requirements to create a new parcel is 10,000 square feet with 50' of frontage along the road. I can calculate parcels that have at least 20,000 square feet with at least 100' of frontage and know that those parcels may be sub-dividable. However, if an already existing structure is right in the center of said parcel then it is no longer sub-dividable without demolishing the structure.

How can I take into account the location of existing structures on a lot to see if the empty space between the structure and lot boundaries are sufficient to sub-divide?

Example of Sub-Dividable Lot:

I think as long as the structure doesn't take up over half the frontage or half the area of the existing lot then you can still subdivide the lot, just maybe not with a single line - you may have to construct a more complex boundary. Is that an additional constraint? — Spacedman, Jul 24 '19 at 17:01
This might help: https://gis.stackexchange.com/questions/147790/checking-if-polygon-fits-inside-another-polygon-using-arcgis-desktop — Emil Brundage, Jul 24 '19 at 17:33
@Spacedman there could be a scenario where the frontage is 100' and the structure is only 40' but it's placed directly in the center. So really there is only 30' on either side of the structure of free frontage. I'd need to be able to determine there is enough consecutive frontage. — David Seroy, Jul 24 '19 at 17:36
You could split that into a U shaped lot that went round the back of the structure, but I guess a contiguous frontage condition is what's missing. But if the structure was 3' back from the frontage you could do a split with two 50' contiguous frontages to the road, just that the new parcel would have a thin section in front of the existing structure... — Spacedman, Jul 24 '19 at 17:41
Or by "frontage" do you mean the parallel projection of any building to the "front" (roadside) of the parcel? Because obviously people don't like other people's stuff between their houses and the road... — Spacedman, Jul 24 '19 at 17:43
If you wish to ask about ArcPy please include a code snippet that illustrates what you have tried and where you are stuck. — PolyGeo, Jul 24 '19 at 20:22
You could test for 100' of total frontage, including at least 50' of unoccupied frontage. You can define "unoccupied frontage" as "no building within the parcel intersects any line drawn perpendicular to the road frontage." Or you can make a more permissive definition, such as, "no building intersects any 50-foot line drawn perpendicular to the road frontage line," where you replace "50-foot" with an acceptable distance between the front of an existing building and any new construction. — csk, Jul 24 '19 at 20:34
What if you created a cutting line that passes through the midpoint of the frontage line segment to the centroid of the parcel polygon? If the line intersects the building footprint, then you could rule it out. — Kirk Kuykendall, Jul 24 '19 at 21:05

FelixIP · Answer 1 · 2019-07-25T01:50:58.730

Simplified approach: - make sure your frontage line is single one per parcel:

densify buildings (clone first) and convert vertices to points
find coordinates of points projection on relevant front line:

lr="FRONTAGE"
def Chainage(id,shp):
    q='"PAR_ID"='+str(id)
    with arcpy.da.SearchCursor(lr, 'Shape@',q) as cursor:
        for row in cursor: 
        geom=row[0]
        L=geom.measureOnLine (shp.firstPoint)
        p=geom.positionAlongLine (L)
        return str(p.firstPoint)
    return -1
#----
Chainage( !PAR_ID! , !Shape! )

Chop frontage by projected points and select longest bit per parcel:

Results can be misleading, e.g. I doubt that a couple of 'high' potential orange parcels can be subdivided into 2 equal parts, but you'll have to inspect much shorter list of candidates.

Note: it is possible to actually subdivide potential candidates, but it will take ages to complete calculations with high resolution results.

Determining if Parcel is Sub-Dividable?

1 Answers1