Cropping a map into multiple pieces with QGIS

This method only requires two steps:

1. Create a vector Grid
   vector>Research Tools>Create Grid
   (it might be good to add a little overlay on each grid)
2. Clip Raster by Mask layer (using vector grid from step 1)
   raster>Extraction>clip raster by mask layer...
   select the green arrow to iterate over every feature in the vector grid, creating a separate clipped raster for each grid square.

Step 1: Step 2: Some outputs visualised over the grid:

My suggestion is as follows:

1. Use the Create grid tool to create a grid for map area.

2. Use the Split vector layer tool to split the data obtained in the previous step into separate files (you will probably need manual editing in this step to correct the borders of the crop area and the map).

3. Use the Clip tool in Batch Process mode to crop the map.