Development Setup

1. Set up a virtual environment, and activate it.

pip install virtualenv
virtualenv venv
source venv/bin/activate

2. Install the requirements.

pip install -r requirements.txt

3. From the top-level directory, install topology in editable mode.

pip install -e .

4. Deactivate your virtual environment once you're done

deactivate

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This is structured into three files:

1. Example.py
2. my_graph.py
3. my_graph_helpers.py

Example.py

Example.py imports a shapefile, finds the roads necessary to create a graph from that, and plots the graph.

my_graph.py

This my_graph.py file includes four classes: MyNode, MyEdge, MyFace, and MyGraph.

MyNode

MyNode is a class that represents nodes. Floating point geometric inputs are rounded to two decimal places¹. MyNodes are hashable.

1. In practice, if the map's base unit is decimal degrees, the two decimal place rounding would be about 1.1 km at the equator, which would cause problems for human scale neighborhoods. Reprojecting the map to meters or km, changing significant_fig to 5, or adding the scale factor (as I've done in the other branch) and rescaling the data appropriately would solve this.

MyEdge

MyEdge keeps track of pairs of nodes as an edge in a graph. Edges are undirected. The geometric length is calculated iff called. Also has T/F properties for being a road or barrier. Hashable.

MyFace

A MyFace is a simple polygon, that makes up part of a planar graph. Has area, a centroid, and a list of nodes and edges. Not hashable.

MyGraph

MyGraph is the bulk of the work here. It's a wrapper around networkx graphs, in order to make the graph explicitly spatial. Nodes must be MyNodes, and are thus located in space, in whatever the map units are and edges must by MyEdges.

All networkx functions are availble through self.G

In addition, explicitly spatial functions for self are:

1. cleaning up bad geometery (using a default threshold of 1 map unit)
2. find dual graphs
3. define roads (connected component bounding edges) and interior parcels, as well as properties to define what nodes and edges are on roads.

Finally, the last code section can break the geomotery of the graph to build in roads, rather than just defining roads as a property of some edges. I don't use this module, but it might be useful someday.

Several plotting and example functions are also included:

self.plot() takes networkx.draw() keywords

self.plot_roads() specficially plots roads, interior parcels, and barriers.

self.plot_weak_duals() plots the nested dual graphs.

my_graph_helpers.py

This file includes a bunch of helper functions for my_graph.py, with a a variety of categories:

1. spatial geometery functions,
2. greedy search probablilty functions,
3. Ways to set up and determine the shortest paths from parcel to a road
4. importing and setting up a mygraph from a shapefile or list of existing faces
5. test functions and test graphs.