  It is often desirable to analyse trajectory data in local coordinates
relative to a reference location. Similarly, temporal data also needs to be
transformed to be relative to an event. Together, temporal and spatial
contextualisation permits comparative analysis of similar trajectories taken
across multiple reference locations. To the GIS professional, the procedures to
establish a reference frame at a location and reproject the data into local
coordinates are well known, albeit tedious. However, GIS tools are now often
used by subject matter experts who may not have the deep knowledge of
coordinate frames and projections required to use these techniques effectively.
  We introduce a novel method for representing spatio-temporal reference frames
using ordinary geographic objects available in GIS tools. We argue that our
method both reduces the number of manual steps required to reproject data to a
local reference frame, in addition to reducing the number of concepts a novice
user would need to learn.
