[Qgis-user] calculating area

[Nik Go]

Thank you all for the tips. I've actually managed to do the same when
I changed the CRS to the appropriate UTM.


On 11/21/09, John C. Tull <jctull at gmail.com> wrote:
> Hi Nik,
>
> On Nov 20, 2009, at 12:04 AM, 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.
>>
>> So, how should I go about doing
>> converting from geographic coordinated to projected coordinates so I could
>> determine/calculate area
>> determine distance between points
>> convert sq. degrees to sq. meters?
>
> You can change your project CRS from the default geographic coordinate
> system of WGS84 to a projected coordinate system based on meters, such as a
> UTM zone. Turn on the "Enable 'on the fly' CRS transformation, and you will
> be set for vector data. If you have raster data, Qgis does not handle on the
> fly transforms on them. For those, I recommend looking at gdalwarp, part of
> the gdal tools. In particular, look at the vrt output format so you do not
> create numerous large file. A vrt invokes gdal to, effectively, perform an
> 'on the fly' reprojection of the original raster data.
>
> Regards,
> John