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Thread: best way to create polygon grid

  1. #1
    j morg
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    Default best way to create polygon grid

    Hello,
    I want to do something that seems like it should be quite simple in ArcMap 10 but keep hitting roadblocks. I am attempting to create a 30x30 meter polygon grid for a given extent. However, so far using the create fishnet tool I keep running into the error of a 2 gb limit on shapefiles. Is there another way I should be going about this. Any help would be greatly appreciated.
    Cheers,
    Derek

  2. #2
    Alexey Tereshenkov

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    Default Re: best way to create polygon grid

    Hi Derek,

    Have you considered using a file geodatabase for output? It does not have this limit on the size of the feature class and provides better functionality. Let us know if you still get an error message when using file geodatabase and what it says.
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  3. #3
    j morg
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    Default Re: best way to create polygon grid

    Thanks Tereshenkov,

    As it turns out the file geodatabase did work a bit better. However, I still seemed to bump up against some limitation with smaller grid sizes across a large are e.g. 30mX30m across a US State. Then I get this error: 001018 : Number of output features exceeds OID limit (2,147,483,647). Is this a way around this?

    Thanks,
    Derek

  4. #4
    Alexey Tereshenkov

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    Default Re: best way to create polygon grid

    Derek,

    I am very surprised that you've got so many output features. I've just run the Create Fishnet tool for the small area (260 sq km) using 30x30 meters cell size. I've got 283,200 output features.

    Let's calculate the number of features for Utah (219,887 sq km). The area I've calculated the fishnet is ca 845 times smaller than Utah. If you'd calculate the fishnet for Utah, you'd get roughly 239,304,000 features.

    The limit for the number of features per one feature class is 2,147,483,647 which is way more than we'd get for Utah. Even Alaska would result in ca 1,869,818,007 features (30x30 m cells). So, either I am doing wrong my calculations or something goes wrong when the tool is running.

    Are you sure you specify the parameters right when running the tool? Number of Rows and Number of Columns parameters should have "0" and Cell Size Width and Cell Size Width should have "30".

    According to the help page, http://help.arcgis.com/EN/arcgisdesk...001r001018.htm, the maximum number of features allowed in a feature class is indeed 2,147,483,647.
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    j morg
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    Default Re: best way to create polygon grid

    Hi Alexey,
    I think your math is correct. And, yes I have the number of Rows and Number of Columns parameters should have "0" and Cell Size Width and Cell Size Width should have "30". The rest of the fields are auto-populated when I choose the Template Extent based on a Polygon shapefile which is in Albers Equal-Area Conic Projection.
    Thanks,
    Derek

  6. #6
    Alexey Tereshenkov

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    Default Re: best way to create polygon grid

    Hi Derek,

    Then it sounds bizarre to me you configure the tool correctly so it should just work. I'm thinking about the template shapefile you specify. You've probably got a good look at this, but just to make sure - does this shapefile feature/features have a proper extent? I mean, could it be that the features are geographically within a small area (only one US state - by the way, which one?) yet the extent of the shapefile is somewhat corrupted and covers a much larger area like the whole USA?

    Could you please test this for me:
    1) Start a new ArcMap session with a new map document. Add your shapefile to the map.
    2) Click on the Full Extent button to see what is the full extent of your shapefile.

    It should take you essentially to the US state overview scale and then you can see if there are any features that are stored far away from the state borders which makes the extent so large (so the fishnet tool is overwhelmed).

    Just another trick which might help:
    1) Create a new file geodatabase and create a new feature class.
    2) Start a new ArcMap session with a new map document. Add the US state borders data and some other data which is relevant.
    3) Edit the newly created feature class, i.e. digitize manually a rectangle around the US state you work with and save edits.

    Try to run the fishnet tool by using the layer in the ArcMap table of contents (which is referencing the file geodatabase feature class we've just edited) in the Template Extent parameter. You can select this layer in the drop-down list of the tool parameter.
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  7. #7
    j morg
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    Default Re: best way to create polygon grid

    Hello Alex,
    The extent of the area on coastal North Carolina (35826 mi²). After verifying that the extent was set correctly with the dataframe properties the tool worked as expected.
    Your feedback helped out a lot.

    Cheers,
    Derek

  8. #8
    Alexey Tereshenkov

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    Default Re: best way to create polygon grid

    Awesome. Glad it worked out well

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