I want to work with a planar coordinate system, and as far as I know QGIS automatically puts me in a cartesian plan if I don't set up a CRS (Coordinate Reference System) for my project. That is exactly what I want.

The issue (may) begin when I import the raster image that I want to work with: it asks me to set a CRS for the image. The same happens when I create a vector layer for drawing features over my raster image: it asks me for a CRS for the vector too. The project remains without a CRS, but untill now I can not put any raster or vector without an CRS.

For tests purposes I set up EPSG:32722 - WGS 84 / UTM zone 22S as the CRS for both raster and vector. I used UTM because I know it is based on a cartesian plan (though I'm not sure it's the best to do).

My goal is to draw some polygons and calculate the area of that polygons. The scale is obtained from my raster (there's an object with known size in the image).

I can't measure correctly the size of my object without setting the CRS of the project to be the same of the raster and vector, so I set the CRS of the project from the layer.

It looks like the area is being correctly measured, but I can't know for sure if some transformation is going on.

That said, my questions are:

Is there a way to import raster or create vector layers without a CRS (am I missing something)?

Are my areas being calculated correctly this way?

Is alright to use UTM for this purpose or there is a better option (maybe define a custom CRS)?

(sorry for my bad English)

QGIS 2.2.0 64 bits on Win 7 64 bits

2 Answers 2


In the GIS world, it is intended that all layers must have a Coordinate reference system (CRS). Without that, the application has no idea how to put various data sources together.

Usually, Raster images have a CRS stored inside. If not, you have to georeference it using known points inside the raster and coordinates form another source. A common way is to load Google or Openstreetmap background with the Openlayers plugin, and georeference on that.

Once your raster is georeferenced, you can create a new vector layer, and digitize the features you want from the raster.

For calculating areas, UTM is surely a good choice.

  • Thanks for the reply, actually my image is not from a geographic location, it is an object which I want to get the area from, and the area will be in cm². I am using QGIS because I know a little bit of it and it is the software that I have now in hands, probably there are other softwares better suited for this work. I use a lot of OpenLayers (awesome plugin, btw) and I know how to georreference images, but unfortunately that's not the case here. Glad to know that UTM is a good choice!
    – elde0618
    Apr 14, 2014 at 19:23

Although any of the UTM systems will work, their false_easting=500000 settings puts the 0,0 origin 500km or (4.487 degrees at the equator) westwards from where the central meridian is conformant to the earth's surface. This normally not a problem but could be an issue if you try to use the geographic features of QGIS.

Alternately, you can create a custom CRS to work in a different projection, such as "Mercator" or "Transverse Mercator" to make coordinates near a 0,0 cm origin conformant the 0,0 lat,lon coordinates.

Under Settings/Custom Projection use the "+" icon, choose a name and "Proj String (Legacy--Not Recommended) like :

+proj=merc +units=cm


+proj=tmerc +units=cm

to choose a simple projection centered on the prime meridian/equator. You can toggle the format back and forth between Proj String and WKT and see the assumptions QGIS will choose, but it's easier to write well-formed Proj than well-formed WKT.

enter image description here

I'm partial to the Transverse Mercator projection (https://proj.org/operations/projections/tmerc.html or https://en.wikipedia.org/wiki/Transverse_Mercator_projection) to help think of the north-south prime meridian as the defining axis, or as bending my cartesian plan view vertically against a globe.

enter image description here

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