Spanish to English Tech/Engineering Construction / Civil Engineering tiling

These are instruction on how to lay floor tile. They're pretty straightforward, but I don't get this. I think they mean the row along the wall or the row before the row along the wall, but can entre mean along??? It could also mean from wall to wall, but then wouldn't it be una franja (not la) and what, then would the franja anterior be? Thanks in advance!

Marcar la franja *entre la pared o franja anterior, y rellenarla con mortero, ir nivelando según nivel