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 ) )

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

http://cran.r-project.org/web/packages/ggplot2/ggplot2.pdf

http://cran.r-project.org/web/packages/ggmap/ggmap.pdf

(Movebank.org) Fuller, M.R., Seegar, W.S., and Schueck, L.S. 1998. Routes and Travel Rates of Migrating Peregrine Falcons Falco peregrinus and Swainson's Hawks Buteo swainsoni in the Western Hemisphere. Journal of Avian Biology 29:433-440.

http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=An_overview_of_geocoding

http://www.cdc.gov/dhdsp/maps/gisx/training/module3/files/2_spatial_analyst_module.PDF