  We define BioScapeL, a stochastic pi-calculus in 3D-space. A novel aspect of
BioScapeL is that entities have programmable locations. The programmer can
specify a particular location where to place an entity, or a location relative
to the current location of the entity. The motivation for the extension comes
from the need to describe the evolution of populations of biochemical species
in space, while keeping a sufficiently high level description, so that
phenomena like diffusion, collision, and confinement can remain part of the
semantics of the calculus. Combined with the random diffusion movement
inherited from BioScape, programmable locations allow us to capture the
assemblies of configurations of polymers, oligomers, and complexes such as
microtubules or actin filaments.
  Further new aspects of BioScapeL include random translation and scaling.
Random translation is instrumental in describing the location of new entities
relative to the old ones. For example, when a cell secretes a hydronium ion,
the ion should be placed at a given distance from the originating cell, but in
a random direction. Additionally, scaling allows us to capture at a high level
events such as division and growth; for example, daughter cells after mitosis
have half the size of the mother cell.
