# Affinity maps and forcefields

I know that before performing docking with AutoDock Vina, we have to compute "vina maps" like below

v.set_ligand_from_file('1iep_ligand.pdbqt')
v.compute_vina_maps(center=[15.190, 53.903, 16.917], box_size=[20, 20, 20])


but I do not quite understand what those maps exactly are. I found from the manual that

...and then compute the affinity maps for each ligand atom types accroding to the Vina forcefield.

but again, what are affinity maps and Vina forcefield. I checked the source code to see that it creates some kind of a grid which will be then used for scoring. What kind of information does this grid data type contains? I would greatly appreciate any help.