topic Re: Proximity Tool Problem (incorrect units) in Mapping Questions

Proximity Tool Problem (incorrect units)

JessicaW — Fri, 24 Jul 2015 20:15:30 GMT

Hello,

I am a total beginner to ArcGIS, I am just using it for a school project.

Question: I loaded a list of longitudes/ latitudes (in decimal degrees) of several subjects in an excel file. I created another excel with just one particular longitude/latitude (in decimal degrees). I added both data excel files into arcgis. I displayed xy coordinates and used the Geographic coordinate system. All the points from both data sets appear on the map.

Goal: I want to find the distance( meters) from all the points in the first excel file in relation to the one data point in the 2nd excel file I added. So, I used the proximity tool, then point distance. I set the first excel data points as my Input feature. I set the data point from the second excel sheet as my Near feature. I set the desired output value for meters.

Problem: When I get the output table of all the distances, they are not in Meters. They are in a decimal form. Maybe because my data is in longitude/latitude decimal degrees? Can someone explain how I can get my distance in Meters?

Re: Proximity Tool Problem (incorrect units)

IanMurray — Fri, 24 Jul 2015 20:47:58 GMT

You will need to project your input data to an appropriate coordinate system that uses meters:

See (copy + paste the url). http://resources.arcgis.com/en/help/main/10.2/index.html#//000800000048000000

The distances calculated by this tool are in the unit of the coordinate system of the input features. If your input is in a geographic coordinate system and you want output distances to be measured in a linear unit (as opposed to decimal degrees), you must first project your input to a projected coordinate system using the Project tool. For best results, use an equidistant projection or a projection intended for your study area (UTM, for example).

Re: Proximity Tool Problem (incorrect units)

DarrenWiens2 — Fri, 24 Jul 2015 20:48:00 GMT

Use the Project tool to apply a projection to your layer. The projection will have a linear unit (e.g. metres) associated with it. When you rerun Point Distance, the units will be in the linear unit of the input feature class.

Re: Proximity Tool Problem (incorrect units)

JessicaW — Fri, 24 Jul 2015 21:28:08 GMT

Thanks. I was reading some other posts that said the same. I was using GCS 1984 because the longitudes/lattitudes were obtained using GoogleMaps.

When I click Projected coordinate system, and then look under UTM, there are SO MANY options. I randomly tried "NAD_1983_UTM_Zone_17N" but when displayed on the map, the points appear near South America. Do you have any idea what specific system I would use if I'm in Tennessee, USA?

Re: Proximity Tool Problem (incorrect units)

JessicaW — Fri, 24 Jul 2015 21:37:20 GMT

Thanks. I'm using ArcGiS 10.2, I don't actually see a Project tool. Once I've added my data, I just right click, hit display xy. A window pops up and in that window I can change the coordinate system to what I want.

Is this what you are referring to?

Re: Proximity Tool Problem (incorrect units)

DarrenWiens2 — Fri, 24 Jul 2015 21:47:51 GMT

No. The pop-up window is where you define the coordinate system of the original data. This can be a geographic or projected coordinate system, but it needs to be the coordinate system that corresponds to the data (e.g. if your data is lat/long coordinates, then you probably want to define a geographic coordinate system, as you've correctly done).

Once you've correctly defined the data, you are free to re-project it using the Project tool in the ArcToolbox section, under Data Management tools -> Projections and Transformations -> Project. Run this tool to translate your unprojected data to a projected coordinate system. ArcGIS will do the math to situate the data in the correct location, but now it will also be in a linear unit, like metres or feet.

Re: Proximity Tool Problem (incorrect units)

IanMurray — Fri, 24 Jul 2015 22:18:02 GMT

I would follow the instructions Darren has laid out for projecting your data. As for which projection to use, I would use either an equidistant projection(keeps distance true), in this case try USA Contiguous Equidistant Conic, or a good local projection would be NAD 83 StatePlane Tennessee FIPS 4100. There is a StatePlane for both units in feet and meters so which you pick is up to you(there is a search bar at the top when you are selecting output coordinate system, I typed all projections as they appear in the list, so they should turn up). Incidentally, Tennessee is in UTM Zone 16N for future reference(fellow Tennesseean here).

Re: Proximity Tool Problem (incorrect units)

JessicaW — Fri, 24 Jul 2015 22:22:43 GMT

Thank you! That helped a lot. So I have to define the coordinate system and then re-project.

I just ran the proximity analysis and the distance output was meters. Yay!

Re: Proximity Tool Problem (incorrect units)

JessicaW — Fri, 24 Jul 2015 22:29:14 GMT

Small world! I just moved to TN for school. I'm just trying to make it through summer research.

Thanks for the suggestions. Greatly appreciated

Re: Proximity Tool Problem (incorrect units)

MelitaKennedy — Fri, 24 Jul 2015 22:29:25 GMT

An alternative to Darren Wiens suggestion to use the Project Tool, is to export the layers in ArcMap to a new coordinate system. The steps are:

1. Add the lat/lon data using the Add XY Data Tool (setting a GCS for the coordinate system)

2. Set the data frame's coordinate system to what you want to use. The suggestion to use the State Plane zone for Tennessee was useful. A UTM zone wouldn't be bad either. No projected coordinate system maintains all distances, and using a small scale pcs like the USA equidistant conic would still lead to distance distortions when used for a smaller area like yours.

3. Right click a layer in the table of contents and select data, export data.

4. In that dialog, set it to use the data frame's coordinate system. Fill out the rest of the information.

Melita

Re: Proximity Tool Problem (incorrect units)

IanMurray — Fri, 24 Jul 2015 22:33:14 GMT

I'm in grad school at MTSU, where are you at?

Re: Proximity Tool Problem (incorrect units)

JessicaW — Fri, 24 Jul 2015 23:02:01 GMT

I'm in medical school at Meharry, but I'm doing my summer research at Vanderbilt

Re: Proximity Tool Problem (incorrect units)

JessicaW — Fri, 24 Jul 2015 23:03:41 GMT

Thanks Melita! I'll try that too.