We report on in situ magnetoresistance measurements of a 30-nm-wide ferromagnetic nanocontact with simultaneous magnetic imaging in the Lorentz transmission electron microscope. The magnetoresistive measurements are correlated with the micromagnetic configuration of the sample. This allows us to assign characteristic features in the magnetoresistance curves to different magnetic configurations of the sample. From our experiments we can conclude that the micromagnetic configuration of the whole sample-not only the nanocontact region-has to be taken into account for the interpretation of magnetoresistive effects or hysteresis loops. Micromagnetic simulations were performed which confirm the experimental results.