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I'm still new in the world of GIS.

I'm currently doing some zonation with "test points." Each has its own coordinates and "P" value. I want to make contours of these data, to divide the whole area into three zones (Yellow zone if P <= 5, Orange zone if 5 < P <= 15, and Red zone if P > 15).

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Please guide me step to step on how to make this with ArcGIS 10 (I don't have a license for 3D Analyst)

Thank you, Best regards.

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Do you have Spatial Analyst? –  Dano Mar 6 '12 at 14:11
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2 Answers

I've not used ArcGis, however I have achieved a similar result with SAGA GIS which is an Opensource GIS application.

http://www.saga-gis.org/en/index.html

Use Gridding to interpolate the point data (B-Spline, Cubic Spline, Multi Level B-Spline...) and then using "Contour Lines from Grid" to convert the grid to contours.

I know its not a direct answer to your question but it giveas you options.

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+1 It's exactly the same as the ArcGIS workflow, so this reply does answer the question (and indicates that there are more ways to solve this problem than IDW interpolation!). –  whuber Mar 7 '12 at 15:40
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Assuming you have Spatial Analyst license:

  1. Interpolation: Spatial Analyst Tools -> Interpolation -> IDW ('Z value field' parameter will be your 'P' field).

  2. Reclassification of interpolated surface into 3 zones: Spatial Analyst Tools -> Reclass -> Reclassify Specify interpolated surface and ranges of desired classes: 0 - 5,...

Now you have a raster which can be symbolized or converted to polygon layer and then symbolized.

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Thank you for your help, I want to ask, in Reclassify window, what's the meaning of "old values" and "new values"? What kind of input to make classes like above, (0-5, 5-15, >15) ? –  Agni Tama Mar 7 '12 at 3:51
    
I want to add some question. I've done all the step that you've described above, and I've managed to get the contour, but still confused in the Reclassify window. The contour generated boundary are limited to the outer points, so it usually makes a rectangular shape. If I have a desired boundary shape, what should I do to get the result just like this illustration: flickr.com/photos/75824480@N07/6960807547/in/photostream Thanks you very much –  Agni Tama Mar 7 '12 at 4:29
    
Reclassification: When you specify 'Input raster' 'old values' are filled with current raster values. 'new values' are integer numbers assigned to range specified in 'old values'. In your case 'old values' will be 0 - 5, 5 - 15, 15 - (max value which appeared in this column). To have only 3 ranges, you should 'Delete Entries' which you don't need. –  Marcin Mar 7 '12 at 7:49
    
Custom boundary (mask): You have to apply it during first process - Interpolation. When you run 'IDW' tool, at the same bottom of the tool window, click 'Environments...' button. In the 'Processing Extent' section specify your custom boundary as an 'Extent'. Then in section 'Raster Analysis' specify this boundary in 'Mask' parameter. –  Marcin Mar 7 '12 at 7:57
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By the way - tools help may be worth reading;) Interpolation overview, IDW, Reclassify –  Marcin Mar 7 '12 at 8:12
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