Overview ¶

This follow-up to the initial grid creation tutorial focuses on building “dynamic grids that are aligned to the lat long graticule.”

Process Steps ¶

Step 1: Create Primary Grid ¶

Establish the foundational grid displaying lines with decimal degree intervals.

Step 2: Create Secondary Grid ¶

Build a second grid layer showing labels positioned at the center of visible grid cells. Configure the offset to half the interval value and disable line rendering.

Step 3: Configure Label Settings ¶

Access label settings for the secondary grid and navigate to custom label configuration options.

Step 4: Expression Builder Setup ¶

In the expression builder’s function editor, create a new function using the code found at the referenced GitHub gist, then save the changes.

Step 5: Enter Expression Formula ¶

Apply the provided CASE/WHEN expression that handles axis-specific labeling:

• Y-axis: Uses alphabetic characters (A-T) derived from grid positioning
• X-axis: Returns numeric values with decimal precision

Key Parameters ¶

The expression references several configuration elements: the composer title, map item ID, grid interval measurements in latitude/longitude coordinates, offset calculations, and the custom Python function for coordinate transformation.

Important Requirement ¶

“The script for labelling assumes that your map CRS is 3857. So it will transform the bounding box from EPSG:3857 to EPSG:4326.”

Users must also assign an Item ID to map elements for proper functionality.