When modeling the emission of light from nanostructures, we typically study either (1) blackbody radiation or (2) dipole emission. For effective analysis, it is important to know how results from these two types of modeling are related. Here, we use Kirchoff's reciprocity to study how interference affects the emissivity and number of emitted blackbody photons from a thin film for varying thickness. Next, we use Lorentz's reciprocity to study how interference modifies the emission rate of a dipole placed within the same film. Finally, to find the connection between these two emission types, we use Kirchoff's and Lorentz's reciprocity simultaneously for an arbitrary three-dimensional large-area nanostructure. We show analytically how the blackbody radiation can be represented as the integrated emission from homogeneously distributed dipoles in the nanostructure. In this case, the dipole moment density is determined by the refractive index of the nanostructure.