[Qgis-user] calculating area

[Micha Silver]

Nik Go wrote:

>
> Hello. I'm trying to calculate area of my shapefiles but I'm not 
> really sure if I'm doing it right.  I expect results to be in meters 
> (sq meters or sq. kilometers) but read out is in sq. degrees.  I'm 
> told that I have shapefiles in geographic coordinate system WGS 84 but 
> I don't know to convert this to a projected coordinate system from qgis.
If your data is in a geographic CRS, then you probably don't want to use 
area calculations. It's best to convert the data to a projected CRS, 
then do the area, length calculations.
Using the fTools plugin:
-  under the Tools->Data Management menu is the tool to "Define the 
projection". Here you can set the projection of your original data to 
WGS84 Lat Lon (EPSG:4326). This is NOT changing your data, only 
declaring its original projection information.
- Now, again under Data Management, choose "Export to a new projection". 
This alllow you to create NEW shapefiles, translated to some projected 
CRS of your choice.
- And next, under the Geometry tools choose "Export/Add geometry 
columns. THis will create a third shapefile, this time with added 
attribute columns. If the shapefile was of polygon (area) features then 
this tools calculates area and perimeter columns for each feature.

Distance between point is another discussion. ;-)

HTH,
Micha

>
> So, how should I go about doing
>
>         * converting from geographic coordinated to projected
>           coordinates so I could
>               o determine/calculate area
>               o determine distance between point s
>         * convert sq. degrees to sq. meters?
>
>
> Thanks
>
>
>
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