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Thread: GIS question - convert polygon to point?

  1. #1
    Cyburbian WSU MUP Student's avatar
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    GIS question - convert polygon to point?

    I have a shapefile with a bunch of parks represented as polygons and I wanted to build a shapefile with the centers of those polygons represented as a point. Is that possible?

    Update:

    I have found that I am able to create a center point for all of the center points combined using the "Mean Center" function in the Spatial Analyst section of the Toolbox but that gives me s single point that is centrally located to all of the polygons. I am instead trying to create one point in the center of each polygon (I have 15 polygons, so I want 15 different points, one in the center of each). I know now that I can make each polygon its own shapefile and then use the mean center function 15 times, but there must be a more efficient way.
    Last edited by WSU MUP Student; 23 Jul 2009 at 10:19 AM.
    "Where free unions and collective bargaining are forbidden, freedom is lost." - 1980 Republican presidential candidate Ronald Reagan

  2. #2
    Cyburbian JimPlans's avatar
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    Absolutely. I've done it in Maptitude many times (i.e. exporting the centroids of areas). In ArcGIS 9.2 (which I assume you're using), it's harder (of course) but it can be done. I'm pretty sure that ArcInfo has this tool built into it natively, but for ArcGIS you need an additional extension. One that you could use is called ET GeoWizards from http://www.ian-ko.com/. While all the "wizards" are not free, some are, including this one.

    I have no comment as to the fact that I can do this natively in Maptitude, but need extra software from a third party to do it in ArcGIS.

  3. #3
    Cyburbian
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    Not sure what version you're using, but in 9.3 (possibly 9.2, but I can't remember), you can use the calculate geometry tool to get the coordinates for the centroid of your polygons. I'm not on a computer with Arc at the moment; so I can't provide as much detail as I'd like.

    Open the attribute table, add two fields (one for the x coordiante, one for the y), and use the calculate geometry tool. Once you have the coordinates, I'm sure there is a way to use them to create a point file. I'll admit it's a little convoluted. JimiPlans is correct in saying there is a built in tool to do this if you have an ArcInfo license The extensions he provided a link to are great. They provide a ton of functionality, especially if you only have an ArcView license. A lot of the tools are free, too.

  4. #4
    Cyburbian WSU MUP Student's avatar
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    I am using 9.3 and I do have an ArcInfo license.


    As for the link that JimPlans provided, I downloaded the tool there and I keep getting an error message when I try to add it to the customized toolbox. It looks like something to do with a missing or different *.dll file.
    "Where free unions and collective bargaining are forbidden, freedom is lost." - 1980 Republican presidential candidate Ronald Reagan

  5. #5
    Cyburbian
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    Ok, with ArcInfo:

    ArcToolBox--->Data Management Tools---->Features---->Feature to Point. Youíll get a point file, and (according to the help files) each point will have the attributes of the polygon it was created from.

    If you have an Info license, I wouldnít worry too much about getting the extension to work. It really seems aimed at helping people with lower license levels gain access to tools that Arc only provides at the ArcEditor or (mostly) ArcInfo levels.

  6. #6
    Cyburbian WSU MUP Student's avatar
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    Quote Originally posted by kpf View post
    Ok, with ArcInfo:

    ArcToolBox--->Data Management Tools---->Features---->Feature to Point. Youíll get a point file, and (according to the help files) each point will have the attributes of the polygon it was created from.
    Perfect! Exactly what I was looking for! Thank you very much!
    "Where free unions and collective bargaining are forbidden, freedom is lost." - 1980 Republican presidential candidate Ronald Reagan

  7. #7
    I need to do the same thing but I have 9.2 and the 'feature to point' option is not there....

    Anyone know how to make it happen?

  8. #8
    Cyburbian
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    Newplanner19, what license level do you have? If you have an ArcInfo license, I believe a comparable tool is available. I think the name might be a little different.

    With a lower license level, you have a couple of choices. You could go the ET Geowizards/GeoTools route (follow the link in JimPlans post). Lots of good, free functionality there. Another option is to use the calculate geometry tool to calculate the x,and y coordinates for the polygonsí centroids, and then use these data to create a point file. This is the method I alluded to in my earlier post. Note, if the calculate geometry tool isnít available (I think itís there at 9.2, but my city upgraded to 9.3 quite a while ago), you can use the regular field calculator; search the help files for the expressions you would have to use. Itís probably better to work with projected data when you do this.

    Open your fileís attribute table, and create two fields (type: double). Name them x_coord, and y_coord (or similar). Select the x_coord field ----> right click ----> calculate geometry ----> select X Coordinate of Center from the dropdown menu. Do the same for the y coordinate. Export the attribute tableís data.Click yes when ArcMap asks if you want to add the data to your project. Right click on the table you just added, select Display X,Y Data. You should now be able to see your centroids. I think the centroids are stored in something like a layer file (it will be named something like filename used to create centroids Event). Youíll have to export this file if you want to make it permanent (i.e. turn it into a shape file, or geodatabase file).

    Itís really not that bad, just a bit convoluted. I wish ESRI wouldnít lock away many of their best tools at the ArcInfo level.

    Sorry if my reply is a bit late. Let me know if you have any other questions.

  9. #9
    BANNED
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    excuse me people

    i have posted this up for a week now

    asking for feedback and input, suggestions, and comments

    other than one or two, i have not received anything

    though my ego says that things are perfect, i know better

    so please, any comments would be greatly appreciated

    even negative ones

    even by kafirs

  10. #10
    Cyburbian Emeritus Chet's avatar
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    Quote Originally posted by stifotflu View post
    excuse me people

    i have posted this up for a week now

    asking for feedback and input, suggestions, and comments
    How is that possible if this is your first post?

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