Intro to GGMAP Emmalee Dolfi

Ethical Implications of Spatial Analysis  Spatially displaying data can change how it’s interpreted  Locational privacy and ethics  Volunteered Geographic Information System (VGIS)  Location-based services (LBS)  Data is often collected without the subject knowing it  Radio Frequency Identification (RFID)  Crime Mapping

What is GGMAP?  Spatial visualization with Google Maps, OpenStreetMaps, StamenMaps and CloudMadeMaps  Combine with GGPLOT2 to spatially display data  Use ggmap() to create basemap layer, use “+” to add ggplot2 layer with data HoustonMap <- qmap("houston", zoom = 13, color = "bw") HoustonMap + geom_point(data=violent_crimes,aes(x = lon, y = lat, colour = offense ) ) HoustonMap <- qmap("houston", zoom = 13, color = "bw") HoustonMap + geom_point(data=violent_crimes,aes(x = lon, y = lat, colour = offense ) )

Geocoding Your Data  Data must be spatially referenced in order to display it using ggmap

The Process of Geocoding  Assigning a location (latitude, longitude) to an address  Compares elements in the given address the reference data set and finds the best match

Getting a Base Map  Get_map() combines get_googlemap(), get_openstreetmap(), get_stamenmap(), get_cloudmademap()  Arguments:  Center, zoom, maptype, color, source

Examples of Maptypes

Displaying Point Data  Geom_point()  Must specify data  Argument: aes()  x = longitude  y = latitude  color = variable to display  If you have factored levels:  Can scale the points based on these factors

Hexagonal Bins  Displays a spatial histogram  Calculates density per bin from point data  Stat_binhex()  Specify data  Need lat and long in aes()  Bins controls the number of bins across the x-axis, which control the size of the bins  Alpha controls transparency

Kernel Density  Calculate magnitude per unit area from point data  Creates equal area cells (like a raster) and gives each cell a value based on the number of point in a “search radius”

References  Michael Mann, Department of Geography, GWU    (Movebank.org) Fuller, M.R., Seegar, W.S., and Schueck, L.S Routes and Travel Rates of Migrating Peregrine Falcons Falco peregrinus and Swainson's Hawks Buteo swainsoni in the Western Hemisphere. Journal of Avian Biology 29:  geocoding  e.PDF