topic Re: Centerline Between Polygons in Geoprocessing Questions

Centerline Between Polygons

MatthewHinton1 — Tue, 14 May 2013 13:21:59 GMT

I am working to find planning jurisdictions for my county. Each city within the county has a 5 mile planning radius, except one which has a 3 mile radius. I have applied the appropriate buffers around each municipality, but I'm hoping to find a centerline between each municipality in areas where their planning jurisdictions overlap. This seems like it would be simple, but it's got me stumped at the moment.

Re: Centerline Between Polygons

DuncanHornby — Tue, 14 May 2013 13:25:50 GMT

What do you mean by centreline? What if you have multiple overlapping polygons, what do you envisage in that scenario? May be you should upload a sketch of what you are after?

Re: Centerline Between Polygons

MatthewHinton1 — Tue, 14 May 2013 13:34:48 GMT

I'm not authorized to upload my work, but I have four polygons, one for each city in my county; none of the polygons overlap. I need to develop a line to divide planning jurisdiction equally between each city where jurisdicitons overlap (polygon).

Re: Centerline Between Polygons

RichardFairhurst — Tue, 14 May 2013 13:49:04 GMT

Well I can say for sure your thought that this is simple is incorrect. It is a complex optimization problem with multiple solutions, which rarely has a clear path, since it depends a lot on the restrictions you want to apply to the solution possibilities. Such problems are much less likely to have a tool that will accomplish the result in one step and you typically have to design a custom solution from combining multiple tools that meet your solution criteria.

For example, is achieving an equal distribution of area more important or an equal distance of separation between boundaries more important. That one choice will have a profound affect on the possible solutions. Equal area is much harder to achieve, because it requires comparisons among several separate output features all of which are unknown at the start, while equal distance from boundaries is much simpler, since it only requires comparisons between input boundariess which are known at the start.

Re: Centerline Between Polygons

MatthewHinton1 — Tue, 14 May 2013 13:57:32 GMT

So hypothetically, if I had two polygons that are 10x10 miles, five miles apart on the same line of latitude, there is no tool that would draw a line exactly between the two polygons at the 2.5 mile "centerline"?

Re: Centerline Between Polygons

RichardFairhurst — Tue, 14 May 2013 14:07:31 GMT

So hypothetically, if I had two polygons that are 10x10 miles, five miles apart on the same line of latitude, there is no tool that would draw a line exactly between the two polygons at the 2.5 mile "centerline"?

I have yet to see a square city, let alone a side by side pair of square cities. If it were that simple I could do it with standard editing tools. Besides boundaries of city spheres of influence are never determined by strict geometric means, they are always determined politically by a body like a Local Agency Formation Commission. A straight line that puts a freeway completely in one jurisdiction's boundary when another city has a legitimate competing interest in that freeway will never be determined to be the legitimate boundary between them simply by considering the degree the line conforms to a geometric calculation.

Re: Centerline Between Polygons

MatthewHinton1 — Tue, 14 May 2013 14:28:59 GMT

I'm working for a city government, so I understand all that. Our governments have agreed to divide jurisdiction by the midway line between cities. That's obviously difficult to get by eyeballing. I have estimated a center line between my city and surrounding cities, but I would rather have something more scientific and exact.

Re: Centerline Between Polygons

RichardFairhurst — Tue, 14 May 2013 14:36:27 GMT

I'm working for a city government, so I understand all that. Our governments have agreed to divide jurisdiction by the midway line between cities. That's obviously difficult to get by eyeballing. I have estimated a center line between my city and surrounding cities, but I would rather have something more scientific and exact.

Agreements like that only last while the line has not been drawn. As soon as it is drawn and the political calculations begin, it will shift. So I would not spend excessive time worrying about survey precision of your line. I guarantee that once politicians actually see the line they will only look at where it falls relative to prime real estate like freeways and business districts and developable areas or expensive barriers like mountain ranges and rivers, etc. to decide how much they will honor that agreement before hiring a lobbyist or lawyer.

Re: Centerline Between Polygons

RobertBorchert — Tue, 14 May 2013 14:38:15 GMT

You wrote that none of the polygons overlap. then you write that you need a line to divide planning jurisdiction equally between each city where they overlap.

Well you could simply create a new set of polygons where the overlap occurs and draw a line equidistant between the edges of the polygon.

I'm not authorized to upload my work, but I have four polygons, one for each city in my county; none of the polygons overlap. I need to develop a line to divide planning jurisdiction equally between each city where jurisdicitons overlap (polygon).

Re: Centerline Between Polygons

RichardFairhurst — Tue, 14 May 2013 14:57:12 GMT

The only tool that might help you if you have an Advanced license is the Collapse Dual-lines to Centerline. But I believe this tool will fail even on actual road casings when the casing lines have widely varying widths over the distance between the ends of the two side by side lines. Increasing the tolerance to the levels that would be required for your problem would also be likely to produce very strange results even if a line was created.

Re: Centerline Between Polygons

ChrisSnyder — Tue, 14 May 2013 17:09:40 GMT

This sounds like a job for euclidean allocation (Spatial Analyst): http://resources.arcgis.com/en/help/main/10.1/index.html#//009z0000001m000000

With some monkey business, this could also be a job for Thiessen Polygons: http://resources.arcgis.com/en/help/main/10.1/index.html#//00080000001m000000

Get your city boundary allocations 1st, then do any buffering (and division of the buffer areas) as a second operation.

Re: Centerline Between Polygons

Rajeshkomte — Fri, 30 May 2014 11:09:56 GMT

Hello all,

guys for the last 2-3 days iam haunted with this question.. "HOW TO DERIVED CENTRELINE FROM ROAD POLYGON". i tried everything shown here but nothing happened.

Re: Centerline Between Polygons

RichardFairhurst — Fri, 30 May 2014 15:11:06 GMT

Hello all,

guys for the last 2-3 days iam haunted with this question.. "HOW TO DERIVED CENTRELINE FROM ROAD POLYGON". i tried everything shown here but nothing happened.

If you have an Advanced license did you try the Collapse Dual Lines to Centerline tool? It has been a while since I tried it, so I don't recall if you have to first apply the Polygon to Line tool or not.

Re: Centerline Between Polygons

Rajeshkomte — Sat, 31 May 2014 03:58:41 GMT

i tried that but its not working for me... can u suggest me a different tool..?

one more thing is there any tool to generate a centreline between polygons.. i have this area polygon shpfile & i want to draw centreline between them.

Regards,

Raj

Re: Centerline Between Polygons

RichardFairhurst — Sat, 31 May 2014 05:04:23 GMT

i tried that but its not working for me... can u suggest me a different tool..?

one more thing is there any tool to generate a centreline between polygons.. i have this area polygon shpfile & i want to draw centreline between them.

Regards,

Raj

There is no other tool. You have not shown a picture of what you are dealing with. Pictures are the only way for anyone to make a better suggestion, but inevitably it will involve perhaps 20 different tools, programming, and multiple iterations. This is an extremely complex and variant objective that no one technique will solve for every case. Although this post about coastline extensions is a different problem, it illustrates some aspects of the complexities of trying to extend boundaries outward from polygons without overlapping existing polygons and the large numbers of tools that are potentially involved to get a desirable result.

I suggest you also show how the tool I suggested did not work for you. If you have actual road casings it should work for the majority of the roads.

Of course real centerlines follow recorded subdivisions and improvement plans and take years to develop for a large jurisdiction, like the County I work for. That is how we did it, but we did it as we developed the parcels, not as an after thought. Anything else is only a hack as far as engineers and surveyors are concerned.

Re: Centerline Between Polygons

RichardFairhurst — Sat, 31 May 2014 06:13:13 GMT

Here is an illustration of a suggested approach for creating non-overlapping buffers. It looks like some of the other posts in this thread have already covered this idea, at least in part (Chris' post), but the illustration shows what is possible.

This post uses tools available from ET Geowizard to create Thiessen polygons from polylines (ArcMap only does this with points. This is most likely what you really need. The complexity of the underlying process is obvious, since he recommends running the Thiessen polygons from lines tool overnight.

Re: Centerline Between Polygons

Rajeshkomte — Wed, 04 Jun 2014 05:16:09 GMT

sorry mates!!! was on a short break 🙂 here iam posting this pics [ATTACH=CONFIG]0[/ATTACH] i want to genrate a centreline between these polygons

Re: Centerline Between Polygons

RichardFairhurst — Wed, 04 Jun 2014 12:58:59 GMT

sorry mates!!! was on a short break 🙂 here iam posting this pics [ATTACH=CONFIG]0[/ATTACH] i want to genrate a centreline between these polygons

The attachment is not working for me. Please post it again.

Re: Centerline Between Polygons

RyanClancy — Wed, 04 Jun 2014 15:32:20 GMT

I haven't tried this, just making it up.

1. Calculate the centroids for each of your city polygons:
    - add two fields of type 'float' to your city boundary polygon table, call them centerX and centerY
    - right click each new field and choose Calculate Geometry
    - for centerX, choose 'X Coordinate of Centroid' and for centerY choose 'Y Coordinate of Centroid'
    - finally, use the Make XY Event Layer tool to create a points layer from these centroids
    - now you have points which represent the geometric center for each of your cities

2. Use the Create Thiessen Polygons tool on your centroid points layer

The resulting polygons should have edges at the mid-points between your cities.

Re: Centerline Between Polygons

Kathleen_Crombez — Wed, 04 Feb 2026 21:26:21 GMT

Did you ever find a solution to this?

We have the same issue where the incorporated municipalities within our county have an agreement in place for future subdivision planning that divides the overlapping 1.5 mile ETJ boundaries with the median centerline. Equal distance from both sides (not necessarily equal area).

I have been banging my head on how to do this with either ArcGIS tools or SQL tools.

This is the best I have come up with so far:

1 - create 1.5 mile buffer around municipal boundary to create the ETJ boundaries.

2 - intersect the ETJ layer with itself (set output type to "INPUT" to create polygons where the ETJs overlap)

3 - use the feature vertices to points tool to create points on the boundary of the overlapping polygons.

4 - create thiessen polygons from the boundary points.

The results are looking good so far... but now I need to convert these polygons into median dissection lines.

Sure... the lines could be manually drawn in... but I am trying to automate this to account for ongoing annexations. I will post an update with my final process once I get it figured out.

In the meantime, I am interested to hear if anyone else has come up with a solid solution.

It seems this is a pretty common approach in government planning to subdivide the ETJs down the median overlap to distinguish future development jurisdiction boundaries.