topic Re: Point Distance Analysis in Geoprocessing Questions

Point Distance Analysis

MeredithLaBeau — Mon, 31 Oct 2011 17:05:08 GMT

I am trying to run a distance analysis on point features to centroids based on a certain class of land area. More specifically, I have all the urban rasters configured to centroid points. Then with another layer of points that are places I would like to analysis the influence of urban area on each of these points, which urban land contributes to each due to the distance, with an obvious cutoff of no more that 15 miles. When I run the point distance analysis it continually fails with a 99999 error. Not sure how to proceed to actually use this tool, does anyone have any suggestions, I would appreciate some advice!

Re: Point Distance Analysis

DanLee — Mon, 31 Oct 2011 20:13:08 GMT

Could you post the two point datasets (urban centroids and places) for us to have a look?

Re: Point Distance Analysis

NobbirAhmed — Mon, 31 Oct 2011 22:06:19 GMT

The Point Distance tool will return distances from each centroid to each of the places within your search radius of 15 miles. If you, for example, have 10 places within 15 miles of centroid 1 then you'll get 15 rows in the output table for that centroid. You'll get kind of a distance matrix but arranged in rows. The Distance field in the output table will show the distance between a centroid and a place. Have you run the tool this way?

Which version of ArcGIS you are using?

Re: Point Distance Analysis

MeredithLaBeau — Tue, 01 Nov 2011 12:25:00 GMT

I am using ArcMap 10 to run this analysis, but you can only run within 15 miles? Is there a number of points you can run the distance too. I am running over 100,000 urban centroids but obviously most are not within 15 miles of the point A, but may be located near point G and so on? I can try to post the datasets.

Re: Point Distance Analysis

MeredithLaBeau — Tue, 01 Nov 2011 12:39:22 GMT

urbans centroids(to large to upload) & pcs points (uppermi_pcs.zip)

Re: Point Distance Analysis

NobbirAhmed — Tue, 01 Nov 2011 15:01:56 GMT

... but you can only run within 15 miles?

I used 15 miles as an example (got it from your first post). If you leave out the search radius (blank) then distances to all places will be calculated.

Is there a number of points you can run the distance too?

Use Generate Near Table tool. Uncheck Find only closest feature and enter the number in the Maximum number of closest matches parameter.

Re: Point Distance Analysis

DanLee — Tue, 01 Nov 2011 16:50:44 GMT

It seesm you are analyzing 26 points (places in your zip file) against 100,000 urban centroid points. Are these two data in the same coordinate system or projection?

Without the centroid data, we can't reproduce/investigate the problem. You can try this workaround:
1. Run Buffer tool with 15 miles distance and the ALL option for Dissolve Type. You should get one multipart polygon.
2. Run Clip tool to clip the centroid points by the buffer polygon.
3. Run Point Distance or Generate Near tool using the places and the clipped centroid points.

Hope you can run through these successfully.

Re: Point Distance Analysis

MeredithLaBeau — Tue, 01 Nov 2011 18:23:34 GMT

Just a question on the generate a near table...Alright for that particular state I have only 26, but others have 100 or so point with one million or so urban centroids. Although not all will be within the radius, as we are at state level. These are both in the same coordinate system. So I clipped the centroids to the ones only within a 10mile buffer of each pcs_point, then I used the tool generate a near table, giving me an output. Some buffers overlay each other due to proximity within a 10mile radius, but when I enter the generate near table, I get one unique value for each centroid. Does this tool only select the nearest centroid to that pcs_point for each centroid?
Thanks

Re: Point Distance Analysis

NobbirAhmed — Tue, 01 Nov 2011 18:49:45 GMT

Does this tool only select the nearest centroid to that pcs_point for each centroid?

How have you set your Find only closest feature parameter? Make sure it is unchecked. Then enter a number for the last parameter Maximum number of closest matches - enter maximum of the numbers, such as, enter 105 from 26, 100, 105.

Re: Point Distance Analysis

MeredithLaBeau — Tue, 01 Nov 2011 18:57:16 GMT

can you clarify that, i have the box unchecked, but why enter only a small number like 105 for 26? I am a bit confused. Thanks for all the help

Re: Point Distance Analysis

NobbirAhmed — Tue, 01 Nov 2011 19:17:41 GMT

...but why enter only a small number like 105 for 26?

Enter the largest of possible numbers you expect. You can enter a very large number if you wish. Just remember that a very large number may take longer for the tool to run. So, be within necessary maximum.

Also, don't enter a radius at this point. Radius takes precendence over the last parameter. You will need to combine this step with the steps proposed by Dan.

So, urban land use centroids are your input features and various places are your near point, right?

Re: Point Distance Analysis

DanLee — Tue, 01 Nov 2011 19:26:15 GMT

I think it is the other way around: places are input_features; centroids are near_features.

If you want distances from a place to all the input points (clipped by a buffer), you only need to uncheck that box. The tool will generate 26 x N records, where N is the number of input centroid points.

The Search Radius controls how far you want to look. Since the buffer/clip process has already given you centroids within the desired radius, your don't need to specify the search radius (note: you mentioned 15 miles, but your buffer distance is 10miles. Should it be 15miles?).

You specify a "Max number of cloeset match" ONLY IF you are not interested in distances for all centroid points, but a certain number, say 5 or 10.

Re: Point Distance Analysis

MeredithLaBeau — Tue, 01 Nov 2011 19:32:23 GMT

Ok let me clarify, I have followed Dan's proposed steps, therefore in another state I have say 223 points (sewerage points), then I have a 10mi dissolved buffer around each of the 223 points, these buffer overlap. Now I want to generate a table to see what urban centroids and we are dealing with 13 million after they have been clipped by the buffer for this state. I want to know which ones are closest to that sewerage point within a 10 mile radius, outside of 10 mi I don't consider it. In addition, on overlapping sewerage sources, I would like to distinguish which urban centroid is closer. Does this make sense, cause eventually, I will introduce more urban centroids to make future predictions on these sewerage sources. So don't I still need to specify a radius when I generate a near table? And then how do I specify maximum, because there could be upwards of 10,000 cells for each sewerage point.
Thanks!

Re: Point Distance Analysis

DanLee — Tue, 01 Nov 2011 23:35:14 GMT

All right, let me try to take you through this again using your new case. Since Generate Near Table tool gives more options that you seem to need than Point Distance tool. I am going to use Generate Near Table tool in the description below.

Your data:
For a particular state you have 223 sewerage points. Let's call it sewerPts.
And you have millions of urban centroid points across many states. Let's call it urbanPts.

Your goal:
"I want to know which ones are closest to that sewerage point within a 10 mile radius, outside of 10 mi I don't consider it".

Normally you should be able to use the Generate Near Table tool, enter 10 miles as the Search Distance, and uncheck the box "Find only closest matches" (unless you only want to find one closest near point to one input point?). The result should contain distances from each sewer point to all those unban points that are within 10miles to the sewer point. If an urban point is beyond 10 miles from a sewer point you won't get a record for it.

If the above process gives you the 99999 error, the workaround I proposed earlier should give you equivalent result. So, here is the updated workaround:

1. Run Buffer tool on sewerPts with 10 miles distance and the ALL option for Dissolve Type. You should get one polygon that contains multiparts. The overlapping boundaries should be dissolved. Let's call it buffer10miles.

2. Run Clip tool to clip urbanPts by buffer10miles. Let's call the result urbanPts_in10miles. This result is equivalent to what would be found by a Search Distance of 10 miles from points in sewerPts to points in urbanPts. So now you have a subset of the original urbanPts, which I hope gives a better chance to run through the next step.

3. Run Generate Near Table tool using sewerPts as input features and urbanPts_in10miles as near features. Enter 10 miles as the Search Distance and uncheck "Find only closest matches". This should give you the desired result. Let's call it sewerPts_urbanPts_nearTable.

You said "In addition, on overlapping sewerage sources, I would like to distinguish which urban centroid is closer". I am not sure if you meant to reverse the analysis - to generate near table from urbanPts to sewerPts within the distance? If an urbar point finds multiple sewer points, you can use the Summary Statistics tool to get the minimum NEAR_DIST value and the corresponding sewer point FID.

I am not very clear about your future prediction part. But unless you want to change 10 miles to a different value, you should run the same process even you include more urban centroid points.

Regarding the "Maximum number of closest matches" option, do you want to find only a certain max number (say 100 or 500) of urban centroid points from each sewer point? If not, don't enter anything here.

I would like to suggest that you test the process by small sample datasets - select 5 sewer points, use a smaller distance so that a small number of urban centroid points are found, and review the table and try to understand and verify the result is expected. Then apply the process to the real data size.

Hope that helps.

Re: Point Distance Analysis

NobbirAhmed — Wed, 02 Nov 2011 15:06:52 GMT

When I run the point distance analysis it continually fails with a 99999 error.

I need to repro the 999999 error you have seen with Point Distance. Could you help by clarifying? Just to be sure - you have few input points (26?)and more than a million near points, right? Which version of ArcGIS you are using? Which OS you are working on?

Re: Point Distance Analysis

MeredithLaBeau — Thu, 03 Nov 2011 21:27:07 GMT

so the workaround seemed to work for all but of a few of the states we are working with. The 99999 or the 99998 error comes when trying to run the generate near table function for states with 16,676,395 or 18,639,934 urban centroid points with about 225 sewerage points. I let the sewerage point be the input features and the urban are the near features, and then I run a 10mi radius, and either I get that error or the table comes up with 0 entries once it is finished processing after an hour. I am running this data on windows 7 with 8GB RAM, and nothing else running.
I appreciate all your help!

Re: Point Distance Analysis

NobbirAhmed — Thu, 03 Nov 2011 21:31:11 GMT

Thanks a lot Meredith. Just the final question: which version of ArcGIS you are using? 9.3 or 10.0? Servicie pack number?

Re: Point Distance Analysis

MeredithLaBeau — Thu, 03 Nov 2011 21:37:48 GMT

I am running ArcGis 10.0 with service pack 3

Re: Point Distance Analysis

MeredithLaBeau — Fri, 04 Nov 2011 17:13:56 GMT

any further advice, since I am still stuck trying to get two states to work...they make be exceeding Arc quota, as one has 18, 639, 000 urban cells with 1150 points to perform nearest function with....?

Re: Point Distance Analysis

DanLee — Fri, 04 Nov 2011 17:49:58 GMT

Are you able to run Steps 1 and 2 of the workaround for these states?

Step 1: Buffer the 1150 points with 10 miles and the ALL option; did you get one buffer with multiparts?
Step 2: Clip the urban cell points by the buffer. Are the 18, 639, 000 urban cells the Clipped result? If not, how many points did you get here?

It may be better that we follow up with investigation outside of the forum. You may contact me at dlee@esri.com. We can give you a site for you to upload your data.

Thanks,