Geometry  _geometry  A surface and/or polysurface and/or mesh for which you would like to conduct the flow path analysis. That can be a building, terrain, landscape or any other sort of geometry.  Goo 
Num Of Initial Pts  numOfInitialPts_  Number of initial points.
Each flowpath has a starting point  a point where a rain hit the ground. numOfInitialPts_ input represents the number of these points, therefor representing the number of flowpaths.

If nothing supplied, numOfInitialPts_ input will be set to 100 (initial points and flowpaths)  Goo 
Initial Pts Spread  initialPtsSpread_  Initial points spread type  choose one of the two types:

0  Rectangular grid (flow paths will start as a regular grid of points)
1  Random (flow paths will start as a random group of points)

If nothing supplied, initialPtsSpread_ input will be set to 1 (Random).  Goo 
Step Size  stepSize_  Step size of each of the flow paths.
Step size can singificantly affect the final flow paths disposition. For smaller scale objects, it is advisable to use smaller step sizes (up to 1). For larger scale objects (terrains with sparse resolution), step size can be increased to more than 1.

If nothing supplied, stepSize_ input will be set to 1 (Rhino documents units: m, ft, in...).

In Rhino document units.  Goo 
Flow Paths Type  flowPathsType_  Choose one of the two flow path types:

0  Polyline
1  Curves

If nothing supplied, flowPathsType_ input will be set to 0 (Polylines).  Goo 
 _____________  Script variable TerrainAnalysis  Goo 
Bake It  bakeIt_  Set to "True" to bake the flowpaths geometry into the Rhino scene.

If not supplied default value "False" will be used.  Goo 
Run It  _runIt  ...  Goo 