We investigated the production of collaborative annotations of maps with mobile devices, looking for the reasons why people might want to produce these notes and how they might do so. We conducted a field trial with 21 participants over 3 months in the center of Geneva, Switzerland. We collected fewer messages than expected and we attributed the reasons for this result with a lack of social conventions surrounding this activity and to the overwhelming effect of the map on participants which caused them to refrain from engaging in content-driven discussions and explorations.