# python-s2g

(S)hapefile (2) Graph/network converter in Python

When we process GIS data, a non-trivial problem is the conversion from shape lines to graph or network data structure. The latter may benefit from these out-of-box graphical libraries such as networkx and igraph. But the conversion is a headache to components open communities. This mostly urges me to finish this tiny but useful library.

# Install

```
pip install -U s2g
```

# Usage

You have two alternative ways to construct the graph. One is reading from a raw shapefiles with `LineString`

objects.
(Under the hood, I involve fiona to read geometries and
shapely to analyze the data.).
Currently, this tool only supports conversion to *undirected graph*.

```
from s2g import ShapeGraph
import networkx as nx
sg = ShapeGraph(shapefile='path/to/roads.shp', to_graph=True)
assert isinstance(sg.graph, nx.Graph)
```

The other way is designed for programmable usage or time-consuming process where intermediate data could be sniffed or saved. Here is an example to read lines with [fiona]:

```
from s2g import ShapeGraph
import fiona
from shapely.geometry import shape, LineString
shp = 'path/to/shapefile.shp'
with fiona.open(shp) as source:
geoms = []
for r in source:
s = shape(r['geometry'])
if isinstance(s, LineString):
geoms.append(s)
# create ShapeGraph object from a list of lines
sg = ShapeGraph(geoms, to_graph=False)
# detect major components
mc = sg.gen_major_components()
# major components are mc[2]
# convert the largest component to networkx Graph
graph = sg.to_networkx() # equivalently sg.graph
```

Dive into source doc to discover other functionalities.

## References

- shp2graph in R by Binbin Lu, as well as his talk on useR! 2011
- A Tutorial on Topology Correction of Shapefiles Using GRASS