The system of Fe on W(001) is investigated using spin-integrated as well as spin-resolved scanning tunneling microscopy (STM). This study ranges from three-dimensional Fe islands down to the Fe monolayer and different growth modes are observed related to the preparation temperature. With scanning tunneling spectroscopy (STS), a layer-dependent electronic structure is observed that can easily be used to assign the local coverage to the investigated sample areas. Spin-resolved measurements of the ferromagnetic layers in the pseudomorphic regime immediately reveal the fourfold magnetic in-plane anisotropy. A direct comparison of the observed arrangement of the domains of the exposed layers shows a rotation of the easy axis from the fourth to the third monolayer and a collinear magnetic alignment of third and second monolayer. This is confirmed by the quantitative analysis of the layer-resolved intensities of differential tunneling conductance. The first monolayer does not show a magnetic component parallel to the surface but has a perpendicular anisotropy. For this layer, measurements with an applied magnetic field prove a c(2x2) antiferromagnetic structure, i.e., a checkerboard arrangement of spins.