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merge mean values from polygons

MalcolmLittle

Hello,

I am attempting to acquire the mean value of an attribute from mutiple polygons that intersect with a regional polygon.

Ex. There are 6 polygons, all with an attribute for Total Clay content (%) but different values. These 6 polygons fall within a county polygon. So essentially I am trying to find out the mean value of Total Clay content (%) for that county.

Is there a toolbox function that can do such a thing?

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Accepted answers

JayantaPoddar

Assumptions: You have 06 polygon feature with clay content. And a county polygon.

Workflow:

1) Clip the Clay_Content polygon features with the county polygon.

2) You need to carry out a formula like below

float((Clay%01 * Area01) + (Clay%02 * Area02) + (Clay%03 * Area03) + (Clay%04 * Area04) + (Clay%05 * Area05) + (Clay%06 * Area06))/(Area_County)

To do the above calculation, you could create a new Field "Clay_Area" (Datatype: Double)

In field calculator,

<Clay%_FieldName> * <Area_FieldName>

Use Statistics/Summarize to obtain the average value of Clay content in the county.

Hope it helps.

Thanks,

Jay

All comments

DanPatterson_Retired

Better still, use USDA classifications (ie clay, silty clay etc) will give you a wider latitude rather than specifying a particular clay content unless you know the clay type and are trying to estimate things like water holding capacity, cation exchange capacity, pH, bearing capacity or similar properties. Regional maps for your area would be your best source and may provide the information that you need to at least compare your site selected results to, to see if they are reasonable.

JayantaPoddar

Assumptions: You have 06 polygon feature with clay content. And a county polygon.

Workflow:

1) Clip the Clay_Content polygon features with the county polygon.

2) You need to carry out a formula like below

float((Clay%01 * Area01) + (Clay%02 * Area02) + (Clay%03 * Area03) + (Clay%04 * Area04) + (Clay%05 * Area05) + (Clay%06 * Area06))/(Area_County)

To do the above calculation, you could create a new Field "Clay_Area" (Datatype: Double)

In field calculator,

<Clay%_FieldName> * <Area_FieldName>

Use Statistics/Summarize to obtain the average value of Clay content in the county.

Hope it helps.

Thanks,

Jay

DarrenWiens2

That's a good point. If so, multiply the percent by the area to a new column (Clay_Area). Then Summary Statistics, Clay_Area = SUM, Area = SUM, County = case field. Then divide Clay_Area_SUM by Area_SUM to get county clay percent. This should work, but it feels like I'm missing a time-saving step.

XanderBakker

Should the percentage be weighted by the area of the polygon?

DarrenWiens2

You are looking for Summary Statistics. Clay content = MEAN, County = case field.

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