Geometries in Python

Geometry, within the context of GIS and Python programming, refers to the points, connecting lines and arrays that compose points, polyline and polygon features.  All of the vector data objects used within a GIS can be expressed in terms of these geometries, which can be easily (relatively speaking) accessed with Python script.

The task at hand for this topic was the creation of a script that output the above- the object ID, a sequential "vertex ID," the x, y coordinates and feature name- all taken from the attribute data of a polyline shapefile of a set of rivers in Hawaii.  The script has to iterate through each line segment and print the coordinates of all of the vertices, placing each pair on a separate line of the text file.  In this process we make use of the concept of the "search cursor" introduced last week, which allows the script to access each row (or record) within the feature class.  Also put into play is the for loop, which provides the means of iteration through each row (in this case each river), and further through each line segment and set of point vertices that compose each one.  The 25 different rivers within the feature class are represented as 25 different object IDs (the first number of the line), with each coordinate pair (vertex) given a sequential ID (the second number), the x, y pair, and finally the feature's name, taken from the name attribute field.  Reading and outputting data such as this from feature classes could be a very useful task for a script to complete, as the required steps, performed manually, would surely become very time consuming, especially if one were working with a large number of datasets.