topic Re: Divide Polygon in equal areas in Data Management Questions

Divide Polygon in equal areas

KonradHentze1 — Tue, 14 Feb 2012 13:06:35 GMT

Dear community,

we are working with a lot of big forest parcels and want to divide them into (exact) 1ha, 0,25ha parcels and so forth. Is there any kind of algorithm which could do this automatically? Up to now, we are overlaying polygon-rasters of smaller size then the desired output and merge the small squares. But of course the parcels we get cant fit 100% in our forest area (squares in irregular polygons). Other solutions are drawing parcels by hand and estimating the area, calculating it as an attribute, take a small bit of or ad a bit and so forth until we get the area of 1 Hectar.

Do you guys have any idea how we can automate this process? and if not as "divide polygon in 0,25 ha pieces" something like " divide polygon in 20 equal areas"? It would save us time and space in our layers :rolleyes:

I fear this is to heavy to calculate but still hope for suggestions

thanks for you input, regards Konrad

Re: Divide Polygon in equal areas

AlexeyTereshenkov — Tue, 14 Feb 2012 16:17:33 GMT

Hey Konrad,

If I got you right, you might like the Create Fishnet tool: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//00170000002q000000

You can choose to create a specified number of rows and columns or specify cell's height and width. Then you specify the extent of your original forest polygon which will limit the output feature class. Do you need to perform any attribute transfer afterwards (i.e., all the attribute a big forest area feature has should be transferred to the output of the tool)?

Let me know if this method works for you.

Re: Divide Polygon in equal areas

KonradHentze1 — Thu, 16 Feb 2012 06:05:46 GMT

Dear Alexey,

thanks for your answer. The fishnet solution is exactly how we are working at the moment. But since the result is a bunch of SQUARES, it usually doesn't fit our IRREGULAR forest polygon 100%. As we are talking of hundreds of parcels we have to work with automatic processes. So I populate a fishnet with the desired area (or smaller and merge them afterwards). Then I clip the fishnet polygons with the forest polygon and delete all parcels which are smaller then the given fishnet area (since they have been clipped). Therefore unfortunately, after cutting all squares which are not exactly 0,25 ha (for example) I have a lot of area which is then classified as not used (see attachment).

Thats why I was asking for a solution which would divide THE WHOLE area in subpolygons, even if they are irregular in their shape. Meaning I would tell Arcgis to divide my forestpolygon of 31,7h ha in 31 parcels (meaning each of them a bit bigger then 1 ha). That would be exactly what we are looking for to avoid gaps at the edges (which can easy add up to some hectares in our case).

I hope I could explain it somehow clear, sorry for my bad written english ...

Re: Divide Polygon in equal areas

AlexeyTereshenkov — Thu, 16 Feb 2012 06:41:31 GMT

Hi Konrad,

I see now. Hm, I believe the only way to do this type of work in an automated fashion in ArcGIS 10 would be using Parcel Fabrics. Check this page to get a general idea what you can do: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//001t000003wp000000.htm. If it is something you want to give a try, I suggest going through tutorial for parcel editing.

http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Tutorial_Getting_started_with_parcel_fabric_editing/001t00000154000000/

The tutorial data is included with ArcTutor which you can obtain when having an ArcGIS Desktop license (contact your distributor if you don't have it). Take your time to learn parcel editing since it is quite large amount of tools and settings there.

If I read things right (have not worked with parcel editing a lot either), then this is the type of task you should look into: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/Creating_new_parcels_using_divide_by_area/001t0000012s000000/

Let me know when you got your hands at parcel editing and if it went well to divide your large forest area as you need.

Re: Divide Polygon in equal areas

KonradHentze1 — Thu, 16 Feb 2012 09:39:13 GMT

Wow! Thanks a lot, thats 100% what we need. Unfortunately, we only have an ArcView License and to upgrade for the Parcels Editor only seems not feasible. I will investigate in all OpenSource solutions and also the free Script which exists for ArcView 3.0 on the ESRI sites.

http://forums.esri.com/Thread.asp?c=3&f=38&t=208496

Thanks again for your helping me with this ...

Re: Divide Polygon in equal areas

KonradHentze1 — Wed, 22 Feb 2012 08:56:25 GMT

sounds weard, but there seems to be absolutely NO solution for this basic problem (apart from the Parcels Editor). I found a commercial extension being able to split a Polygon ONCE. Not feasible though to divide a whole area.
http://www.ian-ko.com/ET_GeoTools/UserGuide/ETSplitPolygonByArea.htm

Any further input will be highly aprreciated guys. Thanks in advance !

Re: Divide Polygon in equal areas

JulianaWilhoit — Wed, 22 Feb 2012 16:49:07 GMT

Hi Konrad,
What version of ArcMap are you using. Based on other forum posts you have made, I am assuming you are using ArcMap 10.0 with an ArcView license. You did, however, say that you were looking for scripts for ArcView 3.0. If you could confirm your version, this would help me in assisting you.

Regards,

Juliana W.

ESRI Desktop Support

Re: Divide Polygon in equal areas

PaulSmith2 — Thu, 23 Feb 2012 01:09:10 GMT

I'm Looking for the same solution. I have irregular Polygons and want to divide into 2 polygons with equal area.

I have ArcGIS 10 and Spatial Analysis. Please advise how I can do this.

Paul

Re: Divide Polygon in equal areas

JulianaWilhoit — Thu, 23 Feb 2012 13:06:49 GMT

Hello,
As Alexey already mentioned, Parcel Editor is probably the best way for you to do this. Parcel Editor is included in the ArcEditor and ArcInfo license level.
You can find out more by reading the page �??About dividing parcels by area in the parcel fabric�?� at http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//001t000003wp000000.htm.

Regards,

Juliana

Re: Divide Polygon in equal areas

KonradHentze1 — Fri, 24 Feb 2012 05:45:43 GMT

Hi Konrad,
What version of ArcMap are you using. Based on other forum posts you have made, I am assuming you are using ArcMap 10.0 with an ArcView license. You did, however, say that you were looking for scripts for ArcView 3.0. If you could confirm your version, this would help me in assisting you.

Regards,

Juliana W.

ESRI Desktop Support

Juliana, sorry for the confusion and thanks for your help. We have indeed an ArcMap 10.0 with an ArcView license only. I found some scripts from Bill Huber (who seems to be the only guy in the whole world wide web who has a real clue about the issue 😄 ) which only work in ArView 3.3 thats why I did some research there as well. But since ArcMap cannot import scripts, its useless.

So I am here, right at the beginning of the story again. Not knowing what to do. I found a PostGIS script which can divide a Polygon in two exact half pieces, but for me thats not enough.

It would be so great if Esri would sell single Toolboxes. We are only interested in this little function, or lets say the parcel Manager. Not the whole Editor or even Info License .... 😞

Re: Divide Polygon in equal areas

JulianaWilhoit — Mon, 27 Feb 2012 13:22:31 GMT

But since ArcMap cannot import scripts, its useless.

Just for clarification, ArcMap does support the use of scripts in languages such as Python and in 10.0 (but not 10.1) VBA.

Have a great day!

Juliana

Re: Divide Polygon in equal areas

DanLee — Mon, 27 Feb 2012 15:44:07 GMT

Hi Konrad,

I don't have an answer to your question, but I need clarifications for future tool design/enhancement.

You seem to think that the "dividing parcel by area" in Parcel Fabric is 100% what you need. I am not an expert in Parcel Fabric, but from reading the help topic and seeing the illustrations, I got the impression that the "dividing parcel by area" divides a parcel into multiple new parcels based on a specified starting direction; so you would end up having one row of new parcels horizontally (west�??east) or vertically (north�??south). Do you need multiple rows and columns of subdivisions as the image you provided shows, which would be a lot more difficult to do?

There are unlimited ways of dividing a polygon into equal-area polygons without the horizontal or vertical constraint. Creat Fishnet tool seems to give you something close; a rotated fishnet may fit more cells depending on the shape of the polygons. But still there could be many ways to divide the remaining border areas where full cells of fishnet cannot fit. Can you illustrate with a drawing how you would resolve those areas? Do you want the dividing lines to follow the same orientation as the fishnet lines, horizontal/vertical or rotated?

The similar questions go to Paul: there are many ways to divide an irregular polgyon into two. Can you give more specifications? Does Parcel Fabric (if you have the right license) give you the right solution? If not, why not?

Thanks for your input in advance.

Re: Divide Polygon in equal areas

KonradHentze1 — Thu, 01 Mar 2012 10:23:35 GMT

Hey, Dan

thanks for your input. Indeed it ist kind of difficult. The ideal output would contain multiple rows and columns. I did not now that the parcel editor would create polygons starting from one direction only. But still it would work for us: We could first divide the are from East to West and then further from North to South. So we would create subareas as long as we would receive our desired output area.

To be honest, at the moment I don't have any solution how to treat the area around the fishnet containing only subsets of squares. One would be to calculate their area and manually merge those ones who make up approximately the same area as one fishnet Square.

regards

Re: Divide Polygon in equal areas

DanLee — Wed, 07 Mar 2012 15:26:29 GMT

Hi Konrad,

Thanks for the feedback. That is a good use of the parcel editor tool; I can imagine that it still requires some manual calculation in order to specify how to divide a parcel. I will keep your case in mind for future automation and tool design.

Re: Divide Polygon in equal areas

LindseyMessinger — Sat, 12 May 2012 17:10:42 GMT

I am also attempting to divide irregular shaped polygons into polygons of equal area. I am doing a research project where I want to sample random areas within a field. I need to generate random points within these fields, one in every 4 acre piece of the field. I could use the fishnet tool to make a grid, however, since the fields are irregularly shaped, this gets complicated at the edges. I know others have suggested using the parcel fabric editor but this seems very complicated and I don't have topology estalished with my fields and am not even sure how to create a parcel fablic from a polygon feature class. Any advice would be apperciated!

Lindsey

Re: Divide Polygon in equal areas

DanLee — Mon, 14 May 2012 18:02:11 GMT

Would you consider keeping relatively larger fishnet polygons (say: > 50% of a full fishnet cell) and eliminating relatively small ones by merging them with neighboring polygons, along the edge? If so, you can try this:

1. Use Select Layer By Attribute tool to select the fishnet polygons if they are < cellsize.
2. Use Eliminate tool (Data Management toolbox - Generalization toolset; ArcInfo license) to merge the selected polygons with neighbors.

Re: Divide Polygon in equal areas

iI — Thu, 09 May 2013 09:49:26 GMT

Good Morning,

We had the same problem and we used the automatic command in Autocad (with APLUS plug-in) called ARED.
To check tutorial about this exact comand called AREA DIVIDE = ARED: https://www.facebook.com/media/set/?set=vb.294901707192311&type=2

Hope it is useful for your problem.

Re: Divide Polygon in equal areas

LisaKing1 — Tue, 09 Jul 2013 16:35:11 GMT

so I have been reading and reading, and I only see in the parcel fabric thing where you can divide 1 selected polygon in the fabric, is that true, I have like 100 I"d like to divide, fishnet doesnt' work because while the polygons are extremely similar, they are sections actually in Ohio, but they are not perfect, so the fishnet ends up not aligning. I just want to divide a bunch of then at once. Am I crazy or is that not possible with fabric tool.

Re: Divide Polygon in equal areas

AaronKing — Fri, 12 Jul 2013 23:21:06 GMT

so I have been reading and reading, and I only see in the parcel fabric thing where you can divide 1 selected polygon in the fabric, is that true, I have like 100 I"d like to divide, fishnet doesnt' work because while the polygons are extremely similar, they are sections actually in Ohio, but they are not perfect, so the fishnet ends up not aligning. I just want to divide a bunch of then at once. Am I crazy or is that not possible with fabric tool.

you are not crazy, and parcel editor wont do a bunch at once, as i understand it.

also, WASSUP CUZ!

Re: Divide Polygon in equal areas

ElliotHartley — Tue, 15 Oct 2013 12:41:36 GMT

Just stumbled on this thread looking for something else... thought I might contribute though.... I can relate to having an ArcMap 'basic'/arcview licence and needing one feature in other licence levels!

You might want to check out the repeating shapes tool here to see if it helps:

http://www.jennessent.com/arcgis/arcgis_extensions.htm

Not ideal but then if we want ideal we have to pay for it 😉