Map labels are smaller in exported image than in print composer

Help! My Map Labels Shrank After Exporting from QGIS!

Ever poured your heart into crafting the perfect map in QGIS, meticulously tweaking labels in the Print Composer until they’re just right, only to export it and… BAM! The labels look like they went through a shrinking machine? Yeah, I’ve been there. It’s super frustrating. Turns out, there’s a pretty common reason why this happens, and thankfully, some easy ways to fix it.

The culprit? It usually boils down to how QGIS handles label sizes and resolution when you export. Think of it like this: the program is doing its best to translate what you see on screen to a static image, and sometimes, things get lost in translation.

DPI and Pixels: A Size-Changing Duo

One of the biggest reasons your labels might be shrinking is the sneaky relationship between pixel-based label sizes and DPI (dots per inch). When you set your label size in pixels, you’re essentially telling QGIS how many tiny dots to use to draw the label. The thing is, the physical size of those dots depends on the DPI. Crank up the DPI, and those dots get smaller, making your labels shrink, too.

Imagine you’re designing a poster. If you print it at a low resolution, the text will be big and blocky. But print it at a high resolution, and everything, including the text, gets much sharper and smaller. It’s the same principle at play here.

The Print Composer often previews your map at one DPI, while the export settings might use something completely different. I remember one time I was exporting a map for a presentation, and the labels were practically invisible! That’s because the export DPI was way higher than what I was seeing in the Print Composer.

Rescue Remedies: How to Keep Your Labels the Right Size

Okay, so how do we stop this label-shrinking madness? Here are a few tricks I’ve learned over the years:

• Switch to Points or Millimeters: Ditch the pixels and use points or millimeters for your label sizes. These are real-world measurements that don’t care about DPI. It’s like telling QGIS, “Make this label this big, no matter what!”
• Tweak the Export DPI: Play around with the DPI setting in the Print Composer’s export options. Lowering the DPI will make your labels bigger, but be careful not to sacrifice image quality. It’s a balancing act.
• “Meters at Scale” or “Map Units” If you want your labels to stay the same size relative to the map, try using “Meters at Scale” or “Map Units.” This ties the label size to the actual geographic scale of your map. Just remember, if your map uses decimal degrees, you’ll need to use tiny numbers for this to work!
• Scale-Aware Labeling is your friend: Get fancy with expressions to dynamically adjust label sizes based on how zoomed in you are. This is super useful for maps that will be viewed at different scales. You can use the scale_linear function to make the label size change smoothly as you zoom.
• Project Variables are cool: Define a project variable for the label font and size. This is a neat trick that lets you quickly change all the labels in your project just by changing one variable.
• XYZ Tile Troubles? If you’re using basemaps from WMS services and the labels are baked into the tiles, try forcing the server to give you a zoomed-out version by lowering the export DPI. Alternatively, try importing the WMS layer as an XYZ tile layer and mess with the zoom levels.
• The Ol’ Increase-Before-Export Trick: Sometimes, a simple workaround is just to make the labels bigger before you export. For example, if you’re exporting at 96 DPI instead of 72 DPI, bump up all your label sizes by about 33%.

Extra Tips to Keep in Mind

• Lock It Down: Once you’ve got everything looking perfect, lock those layers and styles in your Print Composer! This will prevent any accidental changes when you reopen the project.
• Test, Test, Test: Always do a few test exports with different settings to see how the labels look. It’s the best way to find the sweet spot for your map.
• Basemap Blues: If you’re using a basemap, think about using one without labels and adding your own. This gives you way more control over the label size and appearance.

Dealing with shrinking labels in QGIS can be a pain, but with a little understanding of DPI, label units, and map scales, you can conquer this issue and create maps that look fantastic. So, go forth and experiment! Your perfect, perfectly-sized labels are waiting.