get_openstreetmap: Get an OpenStreetMap

Description

get_openstreetmap accesses a tile server for OpenStreetMap and downloads/formats a map image.

Usage

get_openstreetmap(bbox = c(left = -95.80204, bottom = 29.38048, right = -94.92313, top = 30.14344),
    scale = 606250,
    format = c("png", "jpeg", "svg", "pdf", "ps"),
    messaging = FALSE, urlonly = FALSE,
    filename = "ggmapTemp", color = c("color", "bw"), ...)

Arguments

bbox

a bounding box in the format c(lowerleftlon, lowerleftlat, upperrightlon, upperrightlat)

scale

scale parameter, see http://wiki.openstreetmap.org/wiki/MinScaleDenominator. smaller scales provide a finer degree of detail, where larger scales produce more coarse detail

format

character string providing image format - png, jpeg, svg, pdf, and ps formats

messaging

turn messaging on/off

urlonly

return url only

filename

destination file for download (file extension added according to format)

color

color or black-and-white

...

Value

a map image as a 2d-array of colors as hexadecimal strings representing pixel fill values.

Details

this is simply a wrapper for the gui web-based version at http://www.openstreetmap.org/. if you don't know how to get the map you want, go there, navigate to the map extent that you want, click the export tab at the top of the page, and copy the information into this function. the scale argument is a tricky number to properly specify. in most cases, if you get an error when downloading an openstreetmap the error is attributable to an improper scale specification. OSM_scale_lookup can help; but the best way to get in the correct range is to go to http://www.openstreetmap.org/, navigate to the map of interest, click export at the top of the page, click 'map image' and then copy down the scale listed. in some cases the OSM server is unavailable. in these cases you will receive an error message for download.file with the message HTTP status was '503 Service Unavailable'. you can confirm this by setting urlonly = TRUE, and then entering the URL in a web browser. the solution is either (1) change sources or (2) wait for the OSM servers to come back up.

Examples

Run this code

osm <- get_openstreetmap()
ggmap(osm)