Cardmerge

Build multiple 3×4 split cards (left and right halves in one image).
Batch upload maps files in order: 1st, 3rd, 5th… → left; 2nd, 4th, 6th… → right.
Per preview, use the dashed Upload images strip (or drop 2+ images on the preview) to add up to 16 photos; the grid grows rows and columns to fit, in row order.
Add column adds one pane to every row; add row duplicates your current column count. Export stacks rows into one taller image. Use the − controls on rows and on extra columns to drop a row or a column lane.
Each consecutive pair fills one preview; extra previews are added automatically when needed.

Export quality