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I am testing various projections to calculate areas using ICES statistical shapefiles and the QGIS field calculator.

I am using ICES areas downloadable from the following link: http://geo.ices.dk/download.php?dataset=ices_ref:ices_areas. (Please note that the calculations described below made by both ICES and myself were made using a densified version of the data available on the website).

I have been in contact with ICES and they are getting very different results when they calculate their areas using the same projections as me. Can anyone see what I'm doing wrong with my projection or process? To change the projection of my layer I used the 'save as' option to convert it and then imported the new file into my project.

Please see a copy of the layers 'properties' found under the metadata tab all the way at the bottom of this question.

This is what I entered into field calculator: I am certain this is fine.

enter image description here

The results: the left column titled 'Area_km2' represents the correct ICES calculations and the the column on the right titled '3035area' represents my calculations which seem very wrong. Both calculations used CRS EPSG 3035 - ETRS89/LAEA.

enter image description here

Meta data --> Properties:

General Storage type of this layer ESRI Shapefile

Description of this provider

OGR data provider (compiled against GDAL/OGR library version 1.11.0, running against GDAL/OGR library version 1.11.0)

Source for this layer /Users/aninahenggeler/Documents/Humboldt/Thesis /High seas proposal/GIS & Google Earth/ICES/NewICES densified/ICESdensifiedareasclippedat899EPSG3035.shp

Geometry type of the features in this layer Polygon

The number of features in this layer 65

Editing capabilities of this layer Add Features, Delete Features, Change Attribute Values, Add Attributes, Delete Attributes, Create Spatial Index, Fast Access to Features at ID, Change Geometries, Simplify Geometries, Simplify Geometries with topological validation

Extents In layer spatial reference system units xMin,yMin -6150.61,1579195.62 : xMax,yMax 6185275.19,7365876.42

Layer Spatial Reference System +proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs

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    Indeed that was the problem! Thanks a million @Joseph – anina Sep 30 '14 at 17:40
  • Most welcome @anina! I will post the above comment as an answer to hopefully help others in future with a similar problem. – Joseph Oct 1 '14 at 9:40
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Disabling the "on-the-fly" projection setting should yield you the correct results when performing analytics via the Field Calculator:

Project > Project properties > CRS

This bug has been known in early versions of QGIS but has mostly been resolved since QGIS 2.1.

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