[R-sig-Geo] What is the metric projection equivalent to WGS 84

[Jérome Mathieu]

I think you can also use the function

areaPolygon in the R package geosphere,

which doesn't require projected data to calculate the area of polygons (as
far as I understand).

Jerome

2015-05-25 1:35 GMT+02:00 Michael Sumner <mdsumner at gmail.com>:

> On Mon, 25 May 2015 at 06:37 sadaoui <sadaouimahrez at outlook.com> wrote:
>
> > Hello,
> >
> >
> > what is the good  projection to be used, in order to calculate the area
> > (square meters ) of my polygons that are found in different places of the
> > world map.
> >
>
> You can always use Lambert Azimuthal Equal Area (LAEA) for any region - but
> it's best if it's a generally localized area (i.e. no larger than a
> hemisphere) since it's likely the approximations applied to representing
> the polygons won't be robust near the edges (vertices too far apart stray
> from great circles).
>
> This applies generally though, if you have rectangular cells defined in
> longlat not many projections will stay sane unless you have sufficient
> intermediate vertices between the corners.
>
> Safest is to reproject every polygon to its local centre, and use that LAEA
> (+proj=laea +lon_0=centerlon +lat_0=centerlat +ellps=WGS84 for example) for
> individual calculations on each polygon. But it depends on what your data
> are and how they are represented and distributed in space. Given the
> limitations baked into polygon representations it's not possible to give an
> answer that will always work.
>
> There are global projections that are equal area - Sinusoidal and Albers
> Equal Area Conic, but still you can get bitten by topology so checking the
> visually what's happening is important.
>
> These guides might be helpful:
>
> http://egsc.usgs.gov/isb//pubs/MapProjections/projections.html
>
> http://www.georeference.org/doc/guide_to_selecting_map_projections.htm
>
> Cheers, Mike.
>
>
> > best regards
> >
> >
> >
> > --
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> >
> http://r-sig-geo.2731867.n2.nabble.com/What-is-the-metric-projection-equivalent-to-WGS-84-tp7588321.html
> > Sent from the R-sig-geo mailing list archive at Nabble.com.
> >
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Jérôme Mathieu
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