Green areas play an important role in people’s well-being in urban areas. However, traditional survey methods hinder understanding their actual impact. Fortunately, social networking analysis provides valuable information that city planners can use to transform cities and improve city life. This research studies geolocated tweets published in parks, both urban and natural, in Madrid, for their subsequent analysis and classification with machine-learning techniques and determines the emotional impact of green areas on citizens. The main conclusions of this study are that people express more positive sentiments and emotions (i.e., joy and trust) in urban parks in Madrid compared to the sentiments expressed in other areas of the city and a national park in the Madrid region. This positive sentiment is higher in the city’s southern districts and the historical parks. People also tweeted photos more frequently in parks and differences in the topics expressed in the tweets. This analysis can provide additional information to policymakers in urban planning.