Mobile geographic information seeking systems are often employed to support spatial activities in an unfamiliar geographic environment. However, current systems are unable to incorporate the spatio-temporal constraints of these activities in order to support this information seeking. This article describes a methodology addressing the nature of these spatio-temporal activities that has the potential to contribute solutions to this problem. A key element of this approach is the awareness that both the planning and acting phases must be considered in supporting such activities. This means the development of plans that can be amended ad-hoc, whilst still adhering to the spatio-temporal constraints of the activity. The results of such an approach are the ability for a more descriptive representation of a spatio-temporal activity, which can then be used to support spatio-temporal accessibility analyses and disclose geographic information objects that are no longer accessible to the mobile information seeker. The introduction of these spatio-temporal constraints also allows the mobile information seeker to build up an itinerary that adheres to the given spatio-temporal constraints of the activity.