Your data is in place. Everything shows up where it should. Lines are drawn, the base map renders OK, points are projected correctly. The only problem is… you want to show more information for each point than is possible in a single layer. What do you do?

When mapping complex data, a single point often represents multiple pieces of information. One solution to show all this information is to stack copies of the same layer, overlapping symbols. For example, you could map different features of city parks this way:

• Small shape on top, representing an identifying feature (dot for a fountain, triangle for hill, question mark for info booth)
• A background shape to represent staffing levels (circle for unstaffed, or hexagon for daily employees)
• An outer ring that scales in size to show the size of the park
• Color changes to represent maintenance status (green is good, red is bad, black is closed)

This works fine in most cases when arbitrary shapes can be used to represent different classes of data. But what if you need a custom symbol to more accurately represent the function of the location, such as a military base that includes an airfield, barracks and fleet mechanic shop? Stacking symbols of different size, shape and color may confuse the importance and function of each location. It will work, but it won’t be the best representation of the story you are trying to tell with your map.

Sure this symbol might look cool, but what is it really representing? Map readers could easily get confused and frustrated by complicated layers of symbols.

Pictographic symbols like this example are much easier to determine what is happening at that point on the map. These can be displayed dynamically using QGIS.

What’s the Alternative?

GIS software allows custom symbols to be loaded into your map, setting unique symbols for each category of data you specify. This is great! Now each layer copy just needs to be adjusted to show those custom symbols, offset in a such a way they appear next to each other.

But what if you have 20, 50, 100 different custom symbols? Are you going to set each category in each layer copy manually?

NO!

The good news is you can use QGIS to render multiple custom symbols dynamically on the same layer, based on attribute data! With this trick, you can create a multi-symbol visualization of your point data a single location.

Why Use multiple dynamic custom symbols?

It’s simple: this is a game-changing time saver. Using one layer to symbolize everything means you only have one layer to work with for any updates.

• No more guess work on symbol placement. Are the settings the same between all layers? Why does the offset look different? Is the overlap causing a conflict? Did I pick the same color? None of that matters. When you only have one layer to work with, pick your settings once and let the program do the work. If the settings are changed once, all symbols on the map are updated.
• Dynamic symbols based on attribute data means when you update the data, your symbols can automatically update with it. No need to manually pick your custom symbol file, simply save it in an accessible location and let the program find it.

What do you need?

For this process, you only need three things. The example I’m using is a map I created based on American military establishments in France during World War I. The information is taken from My Experiences in the World War by General John Pershing (great book by the way). Here is what you will need to plot dynamically symbolized points:

• QGIS software
• A map with point data that includes multiple attribute fields you want to symbolize all at once
• Custom SVG icons for the park type (e.g., a tree or playground). You can download symbols you like online, or make custom SVG icons yourself (I’ll post a blog later on how to do this).

Step 1: Prepare Your Data

In order to render symbols dynamically, the data needs to include enough information for QGIS to know which symbols will be required for each point. To do this, each point needs to include attributes appropriate for the symbols you want to show. By appropriate, I mean it needs to include a data field for each symbol you will need to show (Four symbols = four data fields). The data for these fields is used to locate symbol files later on, so they must include data representing a file name. I used a text field, but theoretically you could use integers or any other format that could also be used as a file name on your computer.

Example attribute data table. Note the columns “icon1”, “icon2” etc. should contain the file name for the SVG files you will use as symbols.

Step 2: Prepare Your Custom Icons

Before starting in QGIS, ensure your custom symbols are ready. Save each symbol as its own separate SVG file in a folder somewhere on your computer. Save it somewhere you will be able to find, and give every file a unique file name. These file names should match whatever the field values were that you entered in step 1.

Example folder with all custom symbols to be used. Note the file names match the attribute table date from step 1 above.

Once your SVG files are organized, open QGIS and link to this folder by going to QGIS Preferences >System and add the folder path under the section for “SVG Paths.” Now, every time you insert an SVG into QGIS (either symbolizing features on a map, or just a map layout decoration) the folder will be listed as an option to choose those SVG files.

Step 3: Adding Multiple Symbol Layers

To represent multiple variables at one point, you will build an array of symbol layers.

1. Open Symbology: Right-click your layer and select Properties > Symbology. Alternatively you could just use theLayer Styling Panel by right-clicking on any menu and selecting the check box, or going to View > Panels > and select Layer Styling Panel. I prefer the layer styling panel so I can continue working on my map and not need to switch between windows to adjust styles. For me, the Layer Styling Panel creates a quicker, easier work flow.
2. Add Symbol Layers: This sounds unintuitive, but to use this technique, you will choose to style a Single Symbol rather than Categorized or Rule-Based symbols. We will select the custom symbols dynamically later. For our example we are using SVG Markers, choose that from the Symbol Layer Type menu below the symbol tree. Adjust the position of the first symbol by inputting values into the Offset X and Y fields further down the panel. You may need to adjust these again later to make all symbols fit somewhere appropriately. Arrange them in a long row, column, box etc. for whatever looks good to you.
3. When your first symbol is where you like it, add a second symbol layer by clicking the green + (Add symbol layer) button, or the Duplicate Symbol Layer button to the right of the symbol tree. Repeat the offset adjustments to place this symbol somewhere appropriate in relation to the first symbol.
4. Continue to add symbol layers as needed: Repeat the steps above until you have enough SVG Marker symbol layers to represent every data field you need an icon for.

Add several SVG Markers to your symbol layers as needed, and adjust the Size of each symbol.

Adjust the Offset fields for each SVG Marker. Arrange them any way you want them to appear on your map.

Step 4: Driving Symbols with Data

The real power comes from Data Defined Overrides. This allows specific attributes in your data to control the appearance of each symbol layer.

Scroll down near the bottom to the Layer Styling Panel. There should be a field that includes the title of some generic marker shape. Ignore this title. Instead, look to the right of this field to find a button to create a Data Defined Override. We are going to write a series of expressions for QGIS to pick the correct custom symbol for each marker layer. Pick the first marker layer, then click the Data Defined Override button > Edit… This will bring up and Expression Builder window. For each SVG Symbol layer, we will write the expression to check if the matching data field is NULL, and if not, output a file path for the custom SVG file matching the data.

Scroll to the bottom of the symbology settings to find the Data Defined Override buttons (active, highlighted in yellow here).

Add code that tells QGIS to choose a symbol that matches the values in the field. For each SVG Marker, change this code to the corresponding attribute field.

CASE
WHEN "icon3" IS NOT NULL THEN  concat( '/filepath/example/icons/', "icon3" ,'.svg')
END

Step 5: Ignore “NULL” symbols

Oh, I forgot to mention, this technique will work even if some of your points only have 1 or 2 icons to show. For these points, just leave the data in the extra attribute fields as NULL values. At the very bottom of the Layer Styling Panel, the checkbox option for “Enable Symbol Layer” has another Data Defined Override that we will use to help. We will write an expression that allows the symbol to be rendered only if the appropriate field has valid data in it.

CASE
WHEN "icon3" IS NOT NULL THEN
True
ELSE False
END

Step 6: Continue to refine symbol adjustments and enjoy your map

That’s pretty much the whole process. If you need to make changes to the position of any icons, you can continue by adjusting the X and Y offset settings for each symbol layer. If one of the icons just isn’t the right choice for your map, you can easily make the change in one place without needing to update anything else. Simply save a new SVG file in the same folder location as your other icons, and change the file name in the corresponding attribute data fields. QGIS will automatically update the icon based on the dynamic overrides and settings you just chose.

There are some other adjustments that can be done with SVG parameters, such as colors and custom text within the icon. However, I will save that for another post.

Until next time, keep exploring the world around you!

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Welcome to the Northman Sagas presented by Northman Mapping & GIS! This space is dedicated to exploring the vast world of geographic data, mapping, and Geographic Information Systems (GIS). Whether you are a seasoned cartographer or just discovering the power of spatial data, I hope you will find something of value here.

My journey into mapping began with a simple fascination for how spatial data can tell stories, solve complex problems, and visually reveal the hidden patterns of our world. Over the years, that curiosity transformed into a professional passion for GIS software. I created this platform to share that passion with you and to build a resource for others to benefit from.

Moving forward, this blog will serve as a practical, go-to resource for GIS users and map makers of all levels. Here is a look at what you can expect in the coming weeks:

• Tool Reviews: Honest evaluations of various GIS software, web mapping platforms, and plugins.
• QGIS Tutorials: Step-by-step guides tailored for both beginners mastering the basics and intermediate users tackling advanced workflows.
• Data Curation: Curated links and reviews of high-quality, useful public datasets you can use in your own projects.
• Community Highlights: Showcases of inspiring blogs, innovative portfolios, and essential industry resources.

Mapping and GIS is an ever-evolving field. While the focus of most posts around the internet is geared either toward beginner level instruction or advanced, cloud-based database management, my goal is to break down more intermediate level tasks and tools into clear, actionable instructions for the everyday GIS map maker.

Thank you for stopping by for the launch of the Northman Sagas. I am incredibly excited to embark on this spatial journey with you. I hope you find something useful here, and if you have something you want to discuss please reach out!

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