I'm new to QGIS so please bear with me.

I'm using QGIS 3.6. So I imported a CSV-file with latitude longitude coordinates (WGS 84), created markers and set them to have different colors (to show passing of time) and different sizes (to show precision). The accuracy is given in a column in the CSV file in meters, which need to be represented accurately on the map.

I have set it under Layer properties > Symbolizing > Categorized > Symbol > Size > Fieldtype > diameter (my own variable to show the diameter of the circle I want to draw). The problem is that the diameter isn't accurate. The sizes seem more or less correct in respect to eachother but when I use the measuring tool, the lengths are off. I have tried both to set the units as meters to scale and to set them as map units but this doesn't seem to influence the size. I have also tried to use the Assistant function and selecting the same field but even with different scaling methods I cannot get the diameters right.

So what am I doing wrong? Can anyone help me?

  • 3
    "I imported a CSV-file with [...] WGS 84." - There's your error. Map units in a layer's style are based on the layer's CRS. Which currently is not calculating in metres. So save you data in a fitting UTM-CRS, then you're fine. – Erik Feb 28 '19 at 12:53
  • I’m not sure about the translation, so I’ll clarify: "Why are you using the Marker to create circles with a certain diameter, and not use the tool> Buffer>?" – Cyril Mikhalchenko Mar 1 '19 at 18:14
  • @Cyril because markers are used to symbolize which the OP wants to do while buffer will create a new layer. – Techie_Gus Mar 2 '19 at 8:09

If you project your dataset from WGS84 to a projection with meters as the unit of measure you should be fine with doing the steps you've described above. To do this, right click on the layer in the Layer Panel, then choose 'Export'. You can export as a number of filetypes, including .csv if you want to stay in that format. Choose a projection in the dialog box before saving and it will project and save the new file at the same time.

As a side note, if you plan on doing any editing to the file within QGIS, you will want to save as a filetype other than .csv, as you cannot edit a .csv in QGIS.

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