sample_locations_roads: Sample coordinates from roads
In spew: SPEW Framework for Generating Synthetic Ecosystems

Sample coordinates from roads

1 2	sample_locations_roads(place_id, n_house, shapefile, noise = 1e-04, shapefile_id)

`place_id`	numeric specifiying the ID of the region we are subsampling
`n_house`	numeric indicating the number of households
`shapefile`	sp class with all of the locations for each place id. In addition, we must have road shapefiles so shapefile is a list with both the tracts and the roads, tracts is the first object and roads the second.
`noise`	the standard deviation of how much we jitter the road locations in each direction
`shapefile_id`	optionally include a shapefile id for subsetting shapefile