3 replies to this topic

[araki5]

Hi all. I posted this on the ESRI site, but got no answer. Is there a way to buffer from the middle of a poygon?
In other words, I need a point (middle) of a polygon and buffer 20000 ft. from it. Do I need to make a cetroid? Does that make a point in the middle of my feature polygon?

Thx,

[ajbaum77]

Yes you would need to create a centroid then buffer around that. If you are using ArcGIS search for centroid in the help and that will tell you how to find the center of your polygons. Then you will need to export the table with the X & Y fields to t dbf and create an event theme from the X & Y fields then buffer on that.

[Hans van der Maarel]

That sounds like the way to do it. Keep in mind that there's different interpretations of 'center' (center of gravity, centerpoint) and that, depending on the shape, they might actually be outside the original polygon.

[rmcculley]

If you find the centroid, and then buffer, your resulting polygons will be circles. Do you need the buffer to reflect the shape of the original polygon?

In ArcGIS there are two different center points. There is the centroid, which depending on the shape of the polygon, isn't necessarily within the polygon. It is the center of the shape. Then there is the label point, which is a point within the polygon boundaries. If the centroid is within the polygon boundaries, the label point and the centroid are often the same, but no always.