Intro to GGMAP
description
Transcript of Intro to GGMAP
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