Well, centroid of a polygon on a plane, anyway. A polygon on a
Mercator projection would not be quite so easy to calculate a centroid
for if you wanted the centroid of the spherical analog (google
vincenty or haversine for more details). But I guess if all you want
it for is for specifying a label location, you don't care about a
little inaccuracy that varies with latitude, right?
On 2/2/06, n j cox <[email protected]> wrote:
> This is one definition of the centroid, not an approximation.
>
> For some shapes, the centroid might lie outside the area,
> as is true of many a banana state. This can also be true
> economically.
>
> Nick
> [email protected]
> Hoetker, Glenn
>
> I encountered this a while ago and can't swear that I'm remembering
> correctly. However, I believe I found that the (approximate, at least)
> centroid for a region corresponded to the average value of the x_coord
> for that region and the average value of the y_coord for that state.
>
> Friedrich Huebler
>
> > With the -tmap- package from SSC it is possible to create maps in
> > Stata. The help file and user's guide show how labels can be added to
> > a map, with the example of a map of the United States. To add labels
> > it is necessary to specify the x and y coordinates where the labels
> > should be placed. The example database us-database.dta contains the
> > variables x_coord and y_coord that identify the center of each state.
> > Assume that these variables are not present in a database. How could
> > I identify the center of each region where I want the labels to be
> > placed?
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