  AxialGen is a research prototype for automatically generating the axial map,
which consists of the least number of the longest visibility lines (or axial
lines) for representing individual linearly stretched parts of open space of an
urban environment. Open space is the space between closed spaces such as
buildings and street blocks. This paper aims to provide an accessible guide to
software AxialGen, and the underlying concepts and ideas. We concentrate on the
explanation and illustration of the key concept of bucket: its definition,
formation and how it is used in generating the axial map.
  Keywords: Bucket, visibility, medial axes, axial lines, isovists, axial map
