Extracts a list of named OpenStreetMap highways. OSM data are neither
structured nor ordered; this routine reduces data for each given highway to a
minimal number of discrete and sequentially ordered segments. These segments
may or may not connect, yet can be connected at their nearest points with
get_highway_cycle().
Usage
extract_highways(highway_names, bbox)
Arguments
highway_names
A vector of highway names passed directly to the
Overpass API. Wildcards and whitespaces are '.'; for other options see
overpass help.
bbox
the bounding box for the map. A 2-by-2 matrix of 4 elements with
columns of min and max values, and rows of x and y values.
Value
A list of highways matching 'highway_names', each element of which is
a list of distinct components for the given highway.
A list of 2 components:
obj: A data frame of sp objects
warn: Any warnings produced in downloading the data