# How to define an area of 1000 or 10000 ha around a site

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01-16-2020 07:34 PM
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New Contributor

Hi

I have a site (polygon) of irregular shape and need to define an area around that polygon. The buffer only allows to calculate distance from the sides of the polygon. Is there a way to define a buffer based on area or create an area of specific size (say 10000 ha for example ) around a polygon ?

8 Replies
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MVP Esteemed Contributor

If you have a single site... create a new featureclass, draw a rectangle and edit the coordinates of the corners to give you the desired area from your chosen width and height.  You can then shuffle it around and/or rotate it to get the layout you want.   Humanware is going to do a better job in this case

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MVP Esteemed Contributor

Kind of an interesting puzzle! Maybe you could explain your use case (that is, what are you trying to accomplish). I am curious!

Here is a way to create a circular buffer, centered on the centroid of the polygon, of a specified total area outside your source polygon.

Watch your units, if you are using Shape_Area everything should be in map units or square map units (ie feet, meters).

1. Add a field of type Double to your polygon feature class. (xarea)

2. Calculate this field to the area plus your desired buffer area

3. Calculate the radius of a circle for this area, the Python expression would be (math.pi / xarea) ** 0.5

4. Convert your polygons to points with the Feature To Point tool.

5. Buffer these points using the calculated radius value.

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New Contributor

Thanks, looks like yes humanware will be the way here. Just trying to see what constraints are within 1000 ha of my site

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MVP Esteemed Contributor

Does the buffer polygon around the site polygon need to be a specific shape?  For example, Curtis suggested a circular buffer polygon, does that work?  Would a rectangle be better, or worse?

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New Contributor

Would be better if the buffer was the same shape as the site ie same polygon but bigger so to cover a larger area

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MVP Esteemed Contributor

Are you looking for the total area, including the original polygon, to be 1,000 or 10,000 ha or just the buffered area?

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MVP Esteemed Contributor

It can be done

but not without coding.  It entails some work.

• shift the polygon coordinates to the origin by subtracting the center of the polygon from all the coordinates
• from the scaling factor (eg. 2x, 10x whatever) determine the factor needed to scale the coordinates appropriately.
• translate the coordinates back about their original center
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New Contributor

Thank you all, I ended up sorting it out with a CAD offset