QGIS 3.16 – I want to make by 6″x9″ map a 24×36, but all of the text/layers are tiny. Is it possible to automatically scale all of the layers?

Blow It Up! Resizing Your QGIS Map Without a Headache

Ever been there? You’ve slaved over a map in QGIS, got it looking perfect for a small print, maybe a handy 6″x9″. Then, BAM! The boss wants it billboard-sized – a whopping 24″x36″. You export it, and… disaster! All your beautiful text, those carefully chosen line widths, everything’s shrunk to ant-size. Talk about frustrating! You’re probably thinking, “Is there a magic button to just make everything bigger?” Well, not exactly a magic button, but QGIS does have some pretty clever tricks up its sleeve to help you resize your map project without losing your mind (or your eyesight).

The problem, plain and simple, is scale. When you design for a small format, your text and symbols are sized for that scale. Blow it up, and they get lost in the shuffle. It’s like trying to read a newspaper through a telescope – everything’s just too small relative to the bigger picture.

So, how do we fix it? Here are a few ways to automatically scale your layers in QGIS, turning that tiny map into a wall-worthy masterpiece:

1. Atlas: Your Secret Weapon for Layouts

Think of the Atlas tool as a way to “fake it ’til you make it.” It’s not a direct scaling tool, but it lets you re-render your map at the size you need, especially when you’re aiming for a print-ready layout.

• The Gist: Atlas is designed to create a series of maps from a feature layer. We’re going to trick it into making just one map, but at the right size.
• Here’s the Drill:
• First, make sure your map canvas is showing the exact area you want on that 24″x36″ print. This sets the stage.
• Next, create a new print layout. This is where the magic happens.
• Head to the “Atlas” tab in the layout window. Tell Atlas to use a dummy layer – a simple polygon covering your whole map area will do. The trick is, Atlas will only run once, on this single feature.
• Now, add a map item to your layout. Tell it to be controlled by the Atlas. This links the map to that dummy layer, so it shows the right area.
• Here’s the kicker: Set the map item’s “Fixed scale.” This is where you force QGIS to render at the larger scale you need for your 24″x36″ output.
• Because Atlas is running on just one feature, QGIS renders the map at your fixed scale, scaling everything up perfectly!
• Why It’s Cool: Your final layout is spot-on for your target print size.
• The Catch: You have to work within the print layout.

2. Expressions: Your Path to Symbology Superpowers

This is where things get a little geeky, but trust me, it’s worth it. Expressions let you control how your text, lines, and symbols change based on the map scale.

• The Idea: QGIS lets you use formulas (expressions) to define how big your text, lines, and symbols are. By using the @map_scale variable in these formulas, you can make them grow or shrink with the map.
• How To:
• For each layer, open the styling panel.
• For text labels, find the “Size” property. See that little icon next to it? That’s the data-defined override button. Click it and choose “Edit.”
• Now, enter an expression that multiplies your original text size by a scaling factor. Something like this: 10 * (@map_scale / ). Replace 10 with your original text size, and with the scale you used when designing for 6″x9″.
• Do the same for line widths, symbol sizes – anything you want to scale.
• Why It’s Great: You have total control over how everything scales. Plus, you see the changes right in your map!
• The Downside: It takes some expression-fu. And it can be a bit tedious if you have tons of layers.

3. Project Properties: The “Maybe It’ll Work” Option

Okay, I’m not a huge fan of this one for print maps, but it can be a quick fix for simple visualizations.

• What It Does: QGIS has project-wide settings for scale and coordinate systems. Tweaking these might affect your map’s appearance, but it’s not super reliable.
• Give It a Shot:
• Go to “Project” -> “Properties.”
• Mess around with the “General” tab, especially the project scale.
• Why Bother? It’s quick to try.
• Why I’m Skeptical: Results can be unpredictable. Not good for precise prints. Might even distort your map.

Key Things to Keep in Mind:

• Resolution is King: Make sure your output resolution (DPI) is right for your print size. 300 DPI is a good starting point for a 24″x36″ map.
• Test, Test, Test: Export a small chunk of your map at the final size and resolution to make sure everything looks good.
• Font Matters: Some fonts scale better than others. Stick with vector-based fonts if you can.
• CRS is Crucial: Your Coordinate Reference System (CRS) needs to be right for your area. A wrong CRS can mess things up, especially when scaling.

Scaling up a map doesn’t have to be a nightmare. With the right approach – Atlas, expressions, or even a bit of project property tweaking – you can turn that tiny map into a stunning, large-format display. Just remember to test your results and tweak as needed. Happy mapping!