Smell maps are geo-localized representations of the odors present in an environment as perceived by humans. They provide a convenient mean to assess the smellscape of urban areas, determine regions with heavy impact on the population, and measure the reach of industrial emissions. However, their use is not widespread because they are laborious to generate and easily outdated, as they rely on in-place human annotations of the perceived smells. In this work we study the feasibility of automatizing the generation of smell maps by means of a wearable electronic nose (e-nose) as replacement for the human sense of smell; being our main objective the analysis of whether this technology can be employed to map the subjective information inherent in smells. We have collected to that end a dataset composed of more than 450 labeled samples of 10 different smells with a wearable e-nose, and performed a thorough comparison of several machine learning algorithms to evaluate their suitability for this task. As a second contribution, we present a smartphone application developed to record (in situ) e-nose measurements and GPS coordinates as well as the human perception of smells (using a form-based input method). Finally, we present an illustrative example with several automatically generated smell distribution maps and discuss their accuracy.