topic Re: Near Tool in Geoprocessing Questions

Near Tool

ABDALLAMOHAMED — Tue, 10 Jan 2012 18:37:51 GMT

Hello. I used Near tool in ArcMap 10 to calculate the near distnace and I got some fields with zeros value. Then I used the same layer in ArcMap 9.3, and I got near distance field without zeros values. I couldn't figure out the reason for that.Any hint.Appreciate. Thanks1

Re: Near Tool

ABDALLAMOHAMED — Wed, 11 Jan 2012 15:47:20 GMT

Regarding the above post, can any one tell me how to find near distance with out the zero values I'm getting?????Thanks!

Re: Near Tool

DanLee — Wed, 11 Jan 2012 20:27:04 GMT

There are cases where near distance is 0, for example if you have a point inside a polygon, the near distance from the point to the polygon is 0; if you have two polygons that have shared boundary, the distance from one polygon to the other is 0. It would be helpful that you provide more detail about your cases or share a sample data.

Re: Near Tool

ABDALLAMOHAMED — Tue, 17 Jan 2012 18:03:57 GMT

Okay..I have raster layer, and I wanted first to combine cells that are adjacent and diagonal. To do so , I used Region Group with option �??EIGHT�?� , �??CROSS�?� option for zone grouping method. Secondly, I wanted to derive the nearest distances for each polygon. So I converted the resulting raster to polygon. Then I used the NEAR tool to get the nearest distance. The problem is I'm getting Near distance with zeros values, which shouldn't be so. So the problem is how to get rid of these zeros, or my model might be from the beignning was wrong, don't know..Any hint on that..Appreciate...

Re: Near Tool

DanLee — Tue, 17 Jan 2012 20:18:24 GMT

Have a look of the Generate Near Table tool, which allows you to specify a Max. Number of Closest Matches. You can specify a number and delete the ones of zero values in the result. You may need to run the Summary Statistics to get the minimum values if you find more than one near features for each polygon.

Re: Near Tool

ABDALLAMOHAMED — Wed, 18 Jan 2012 14:14:55 GMT

Dan.. Thanks for your input..I have more than half a million records, and so deleting the zeros is not practical, Plus having zeros is an indication that there is something wrong going on. Because to my knowledge the Near distance shouldn't be zeros. There should be a distance between one polygon and another.. Don't know..
Thanks!..

Re: Near Tool

DanLee — Wed, 18 Jan 2012 14:44:09 GMT

Would you be able to share a sample data - a few polygons that you get zero for NEAR_DIST - so that we can investigate what may be wrong?

As I said earlier, if two polygons are touching or intersecting, the near distance from one to the other is zero. Are you saying that your polygons are not touching and you get zero near distance between them? What is the XY Tolerance of your data (check the properties of your feature class)? Did you set the XY Tolerance.

Oh another thing: is your data projected? If not, meaning they are in decimal degrees, then the near_dist will be in decimal degrees and very likely with zeros. You would need to apply an appropriate projection so that your features would be in meters or feet for the proximity analysis.

Re: Near Tool

ABDALLAMOHAMED — Wed, 18 Jan 2012 15:26:28 GMT

Dan..Thanks for your message.The table below shows the polygons having near distance zeros. I also attached a file with this message showing sample of these polygons. It is true that some of the polygons are touching each other. I was trying to fix that by using the Dissolve tool, but didn't work well in getting rid of the touching. Also my data is projected in meters so no problem with that..Let me know. Thanks a lot!

FID Shape IDGRIDCODE NEAR_FID NEAR_DIST
68 Polygon 69 2011 70 0
70 Polygon 71 2011 68 0
72 Polygon 73 2011 70 0
79 Polygon 80 2011 72 30
80 Polygon 81 2011 84 0
84 Polygon 85 2011 80 0
88 Polygon 89 2011 92 30
91 Polygon 92 2011 99 42.426407
92 Polygon 93 2011 96 0
96 Polygon 97 2011 92 0
99 Polygon 100 2011 96 0
101 Polygon 102 2011 99 0

Re: Near Tool

DanLee — Wed, 18 Jan 2012 15:35:02 GMT

Did you attach the sample data?

Re: Near Tool

ABDALLAMOHAMED — Wed, 18 Jan 2012 15:41:05 GMT

Yes I did but don't know if i did it right or not.I clicked on manage attachments and then I attached the file..

Re: Near Tool

DanLee — Wed, 18 Jan 2012 15:47:25 GMT

I still don't see it. You can try to email it to me: dlee@esri.com

Thansk.

Re: Near Tool

ABDALLAMOHAMED — Wed, 18 Jan 2012 15:52:25 GMT

I just sent it to you email..
Thanks!

Re: Near Tool

DanLee — Wed, 18 Jan 2012 16:33:50 GMT

Thanks and I received the jpg image.

These touching cases are very much of the effect of raster/grid to vector/polygon conversion. You may consider the following options:

1. There is an Aggregate Polygons tool (Cartography - Generalization in ArcGIS 10; previously in Data Management - Generalization). You can try a small distance and see if the touching polygons become connected.

2. Or, if you want each group of touching polygons to merge into a new polygon, you can use the Buffer tool with a VERY small buffer distance (0.2 meters?). The resulting shape will be slightly enlarged and the corners become round, but the touching polygons will be connected with a small "width".

3. If you want the touching polygons to become disconnected, you can use the Buffer tool with a VERY small negative buffer distance (-0.2 meters?). Each resulting shape will be slightly smaller.

You can actually use the zero near_dist to select the touching polygons and apply one of the above ways to them only. Hope the slight gain or loss in shape_area is acceptable.

Hope this helps.

Re: Near Tool

ABDALLAMOHAMED — Wed, 18 Jan 2012 17:03:41 GMT

Let me try them and let you know.
Thanks a lot..

Re: Near Tool

ABDALLAMOHAMED — Mon, 23 Jan 2012 16:37:37 GMT

Dan..None of the above gave me the required result..I couldn't get the touching polygon to disconnect or aggregated in one polygon..Any hint? appreciated.

Re: Near Tool

DanLee — Mon, 23 Jan 2012 17:04:06 GMT

The buffer approach should work. Did you zoom in to a touching spot to see?

Otherwise, can you share a small sample data, as shown in the image you sent me? You are using ArcGIS 10 with an ArcInfo license, correct?

Re: Near Tool

ABDALLAMOHAMED — Mon, 23 Jan 2012 17:19:07 GMT

The buffer didn't work, because when I run the Near tool still getting zeros distance. Yes I'm using ArcMap 10.. I selected near distance with zero values and i will try to send you the layer in your email..
Thanks!

Re: Near Tool

ABDALLAMOHAMED — Mon, 23 Jan 2012 17:23:11 GMT

I just sent you sample data in your email..Let me know if you receive it..
Thanks..

Re: Near Tool

DanLee — Mon, 23 Jan 2012 18:01:00 GMT

No, I have not received your data. Did you send it to dlee@esri.com? Did you get a return error? Try to send me an email without data first.

Re: Near Tool

ABDALLAMOHAMED — Mon, 23 Jan 2012 18:19:52 GMT

I just sent you the whole shapefile in three different emails.. Because of my limit, I couldn't it in one email..I hope you have recieved it..please let me know..
Thanks!