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Thread: latitude of north and south boundary of a polygon

  1. #1
    Elaine Kuo
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    Default latitude of north and south boundary of a polygon

    Hello,

    I have some polygon shapefiels.
    Each of them are composed of more than one polygon.

    I would like to ask how to get
    1. the latitude of the north boundary of the northmost polygon in each shapefiles.
    2. the latitude of the south boundary of the southmost polygon in each shapefiles.

    Thanks.

    Elaine

  2. #2
    Tim Hopper
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    Default Re: latitude of north and south boundary of a polygon

    Elaine,

    Here's a crazy idea. It will require an ArcInfo license. If you don't have an Info license, there may be another way around but I'd have to think about it.

    1. Run the Minimum Bounding Geometry GP tool on your polygon shapefile.

    Use the RECTANGLE_BY_AREA type and set the group option to ALL.

    This will give you a single polygon which encompasses all of your polygons. Theoretically, the top and bottom of this polygon should be the numbers you're looking to obtain.

    2. Run the Feature Vertices to Points GP tool on the output from step 1.

    Use the point type of ALL.

    3. Run the Add XY Coordinates GP tool on the output from step 2.

    4. Run the Summary Statistics GP tool on the point shapefile which you just added XY coordinates to.

    You will need to add the POINT_Y field twice to the "Statistics Field(s)" section. For the statistic type, choose "MIN" for one and "MAX" for the other.

    You'll end up with a table that contains two fields, one containing the northern latitude of the extent of the shapefile and another containing the southern latitude of the extent of the shapefile.

    Just a thought.
    Tim Hopper
    GIS Specialist
    Baxter & Woodman Consulting Engineers
    Esri Certified ArcGIS Desktop Professional

  3. #3
    Tim Hopper
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    Default Re: latitude of north and south boundary of a polygon

    And now that I'm thinking about it...

    No need to do step 1 to get the envelope. Just start with step 2 on your polygon shapefile.

    Throw those tools in a model and you've got an easy way to get the values you're looking for.
    Tim Hopper
    GIS Specialist
    Baxter & Woodman Consulting Engineers
    Esri Certified ArcGIS Desktop Professional

  4. #4
    Elaine Kuo
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    Default Re: latitude of north and south boundary of a polygon

    Thanks for the response.
    It is a great idea

    sorry I forgot to mention that I am using ArcGIS 9.3


    Please kindly help with the questions

    1. Are step 2 to 5 also available in ArcGIS 9.3?

    2. There for about 500 polygon shapefiles to be dealt with.
    In addition to modelbuilder, do you advise any other efficient tools for the process you mentioned?

    3. There are more than one polygon in each shapefile.
    In each polygon shapefile, polygons are classified by the season S and W.
    Please kindly advise any insight if latitudes of north and south boundary of S and W polygons need to be obtained respectively.

    Thanks again.

  5. #5
    Tim Hopper
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    Default Re: latitude of north and south boundary of a polygon

    Piece of cake, mostly...

    1. All of the tools mentioned above are available in 9.3. Feature Vertices to Points requires an ArcInfo license.

    2. You'll need to use iteration to run the process on all of the shapefiles in a folder. Unfortunately, at 9.3 iteration in model builder really isn't an easy thing to do. At v10.0 there are new iterators which can be used in models which make it much easier. Your best bet is probably to use python instead (perhaps you have someone that could help with this if you don't have python experience?).

    3. For calculating these values for both feature types (S and W), just use the "Case field (optional)" at the bottom of the Summary Statistics tool. Input the field that contains the S and W attributes and you will get the MAX and MIN Y values for each unique value that it finds within that field.
    Tim Hopper
    GIS Specialist
    Baxter & Woodman Consulting Engineers
    Esri Certified ArcGIS Desktop Professional

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