Map Icons

How to Use

Add the Icons to QGIS and integrate with OSM Data

The code provided is used within QGIS’s Expression Builder to control the size of the symbols representing the centroids of features based on the map’s scale and the area of the features. Here’s a breakdown of each part of the code:

min(
    max(
        sqrt($area) / (@map_scale / 2500) * 0.2,  -- Increased scaling factor for larger size
        12  -- Increased minimum size for better visibility when zoomed in
    ),
    60  -- Slightly increased maximum size for larger appearance when zoomed out
)

• sqrt($area): This function calculates the square root of the area of the feature. Taking the square root helps in reducing the range of area values to a more manageable scale, which aids in more uniform symbol sizing.

• @map_scale / 2500: Here, @map_scale refers to the current map scale. Dividing this by 2500 adjusts the scale factor so that the symbol size calculation is balanced against the actual size of the map being viewed.

• * 0.2: This multiplication factor adjusts the scaling further, tuning the overall size of the centroids to ensure they are neither too large nor too small across various map scales. The value 0.2 can be adjusted based on specific visualization needs.

• max(..., 12): The max function ensures that the calculated size never falls below 12mm, which helps maintain visibility when the map is zoomed in.

• min(..., 60): Conversely, the min function caps the maximum size at 60mm to prevent the centroids from becoming too large when the map is zoomed out, ensuring that the map remains uncluttered and visually appealing.

• Open Layer Properties: Right-click on the layer for which you want to set the centroid size and select Properties.

• Navigate to Symbology: Go to the Symbology tab within the Layer Properties dialog.

• Set Size Expression: Find the size setting for your centroid symbol and click on the expression editor button (it looks like an “ƒx” symbol). Paste the provided code into the expression editor.

• Save and Apply: Confirm your settings by clicking OK or Apply. The map will now render the centroids using the sizes calculated by the expression based on the current zoom level and the area of each feature.