[Qgis-user] convert the area from 1 sq degrees to hectare

[Micha Silver]

On 08/07/2010 11:31 AM, herman palaquium wrote:
> glad to see you again
>
> as you know that my places at N-E of the year ( please type buol 
> indonesia on the google maps) I STAY THERE
>
> i remember that you give me the answer before, but CAN YOU GIVE 
> FORMULA HOW TO CONVERT 1 SQ DEG. TO ...... HECTARE ..?
You can *not* just convert degrees to hectares in a Lon/Lat projection. 
The rough figures I sent last time were just an inaccurate estimate.  
Afterall, as you move north or south towards the poles, the width of 1 
degree changes in size.
What you should do is re-project your data to some projected coordinate 
reference system. Then units will then most likely be in meters, and you 
can calculate areas very simply. I see [1] that Indonesia uses a set of 
Transverse Mercator projections. You might chose the one relevant to 
your area.

In QGIS:
* you can project a shapefile to another CRS by using the "Save As" 
option, and select whatever export CRS you want.
* Rasters can be re-projected using the Raster Tools plugin, gdalwarp tool.

[1]  http://www.spatialreference.org/ref/?search=indonesia

-- 
Micha

>
> PLEASE STEP BY STEP FORMULA YOU TYPE IT, FOR I KNOW THE WAY OF FORMULA 
> FUNCTION
>
> I HOPE GREATEST THAT KNOW FOR MY STUDY
>
> SALAM HORMAT
> HERMAN DARI INDONESIA
>
> On 27 Jun 10, at 0:47, Nicklas Avén wrote:
>
>> Hallo
>>
>> hmm, is this right Micha. Isn't the size of a sqare degree depending 
>> on how far from equator it is. Since the vertical longitudes are 
>> convergating to the poles 1 west-east degree is 0 at the pole and 
>> about 40000/360 km at the equator which makes the conversion difficult.
>>
>> /Nicklas
>> ----- Ursprungsmeddelande -----
>> > On 06/26/2010 03:40 PM, herman palaquium wrote:
>> > >
>> > > AREA: 2.7e-05
>> > > KebunPoly: KebunAmran1
>> > > Luas: 0
>> > > PERIMETER: 0.024863
>> > > Panjang: 0
>> > >
>> > > please help the area and perimeter unit
>> > >
>> > The numbers above indicate area: 0.000027 square units.
>> > If, by mistake, you projection units is degrees, instead of meters, 
>> then
>> > this would be 0.000027 square degrees. One sq deg ~= 110 km X 110 
>> km, or
>> > about 12,000 sq km. So the above would translate to approximately
>> > 327,000 sq meters. Does that make more sense?
>> >
>> > Again, if your units are degrees, not meters, then the perimeter would
>> > be around 2,730,000 meters. (110 km/deg X 0.2483 )
>> >
>> >
>> > > my projection is meter
>> > >
>> > > where is the correct 2,4863 meter
>> > >
>> > > or 24,863 meter
>> > >
>> > > or 248,63 meter
>> > >
>> > > or 2486,3 meter
>> > >
>> > > or 24863 meter
>> > >
>> > > or any answer the correct
>> > >
>> > > and than
>> > >
>> > > where is the correct area answer ?
>> > > 0,27 ha
>> > > 2,7 ha
>> > > 27 ha
>> > > 270 ha
>> > > or any answer the correc
>> > >
>> > >
>> > > herman
>> > > indonesia
>> > > _______________________________________________
>> > > Qgis-user mailing list
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>> > >
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>> > >
>> >
>> >
>> > --
>> > Micha Silver
>> > Arava Development Co. +972-52-3665918
>> > http://www.surfaces.co.il
>> >
>> >
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>>
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-- 
Micha Silver
Arava Development Co. +972-52-3665918
http://surfaces.co.il


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