GIS frequently asked questions

I'm getting an error when I try to assign a projection, or reproject a layer in QGIS. I'm using a Mac.

Problem

When you try to run the Assign Projection or Warp tools in QGIS, you get an error which says "ERROR 1: PROJ: proj_create_from_database: Cannot find proj.db". The tool doesn't correctly reproject your layer.

Solution

This seems to be a problem with particular versions of QGIS on a Mac. There is a page about the proj.db problem on the web.

The possible solutions appear to be:

• Install a version of QGIS newer than 3.26. So as of February 2023 try installing version 3.28.
• Or use the Python console to link to proj.db by:
• Open the Python console by going to Plugins > Python console.
• When it opens, type in the two lines of code below:

		import os

		os.environ["PROJ_LIB"]="/Applications/QGIS.app/Contents/Resources/proj"
	    

I can't run the Fix Geometries tool successfully. I'm using a Mac.

Problem

Sometimes you need to run the Fix Geometries tool before being able to use some selection or extraction tools, such as Intersect, Select by Location or Extract by Location. Unfortunately, on a Mac, this is causing an error and not running.

Solution

Unfortunately this seems to be a problem with Mac not having an updated QGIS package. There doesn't seem to be a solution at the moment (March 2023), but we'll keep an eye on the Github page about the error.

Until a solution becomes available, all I can suggest is that you try the selection/intersection/extraction tool without using fix geometries. Sometimes this will work. If you get an error telling you that you need to fix geometries, then I'm afraid the only solution I can suggest for now is to log on to a Windows computer in a cluster to run this part of the processing.

My panels have disappeared in QGIS

Problem

You've been using QGIS, and have managed to close one of the panels, such as the Browser or Layers panel. How do you get these back again?

Solution

It's very easy to close panels by mistake, and once you know how, it's also very easy to get them back.

Go to View > Panels on the menu bar and put a tick in the box next to the panel(s) that is missing. It should reappear.

A similar thing works for toolbars too. Go to View > Toolbars on the menu and click the correct box.

I'm importing a spreadsheet with numbers. I'm changing the type to a number, but the fields are still importing as text.

Problem

There seems to be a problem with the Spreadsheet plugin at the moment. Even if you change columns to a numerical type, such as Real before you import them, they are still text once imported. This means you can't then use them in the Field Calculator to create a Total column.

Solution

You can correct this problem by using the Refactor fields tool. Search for Refactor in the Processing toolbox. Once you open that tool you can change field types, so change the fields to Decimal (double) or Integer (if you don't have decimal places) and you should be able to use the field calculator on them.

How do I add a copyright symbol to layout text?

Problem

You're adding a copyright acknowledgement to your map and need to use the copyright symbol - ©.

Solution

The solution to this depends on whether you are on a Mac or PC.

• On a Mac, use the shortcut 'Option + G'.
• On a Windows desktop, make sure you're in the text properties box, not on the layout itself, then with the number lock on, hold down the Alt key, and type 0169 on the number pad.
• If you are on a Windows laptop and don't have a number pad, type [%char(169)%] into the text properties box instead.

Some processing tools are failing with an error if I try to save the output to a temporary layer.

Problem

When running a processing tool in QGIS and generating a temporary layer as output, the tool fails with an error and doesn't generate the output layer(s). The error message says something about a particular file not being specified. If you run the same tool with exactly the same parameters, but save the output to a file, it works with no problem.

You can get around this easily when running individual tools, just by saving the output to file, but if building a graphic model it isn't possible to use the output of one algorithm as the input to another.

Solution

The solution appears to be to change the default output extension in the QGIS options as this may be set to a format such as xtf.

In QGIS, go to Settings > Options. Look for the Processing tab and click on the General subheading at the top of that page. Next to Default output vector layer extension type gpkg. It's also worth checking the default output raster layer extension is set to tif.

I've scanned my geological field slip and it's in pdf format, but now I can't add it to GIS to georeference it.

Problem

As you've discovered QGIS won't allow you to add pdf files to a map. You need to convert the pdf to png, tiff or jpg formats - any of which will be fine.

Solution

Either rescan the document and select jpg or tiff output, or (and this may be the simpler way to do it!) use one of the many online converters. smallpdf.com is easy to use. It can convert between pdf and various file types including jpg.