Transcript Intro_to_ggmap

Intro to GGMAP
Emmalee Dolfi
Ethical Implications of Spatial Analysis
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Spatially displaying data can change how it’s interpreted
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Locational privacy and ethics
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Volunteered Geographic Information System (VGIS)
Location-based services (LBS)
Data is often collected without the subject knowing it
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Radio Frequency Identification (RFID)
Crime Mapping
What is GGMAP?
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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
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Data must be spatially referenced in order to display it
using ggmap
The Process of Geocoding
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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
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Get_map() combines get_googlemap(),
get_openstreetmap(), get_stamenmap(),
get_cloudmademap()
Arguments:
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Center, zoom, maptype, color, source
Examples of Maptypes
Displaying Point Data
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Geom_point()
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Must specify data
Argument: aes()
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x = longitude
y = latitude
color = variable to
display
If you have factored
levels:
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Can scale the points
based on these factors
Hexagonal Bins
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Displays a spatial histogram
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Calculates density per bin
from point data
Stat_binhex()
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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
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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
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Michael Mann, Department of Geography, GWU
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http://cran.r-project.org/web/packages/ggplot2/ggplot2.pdf
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http://cran.r-project.org/web/packages/ggmap/ggmap.pdf
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(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.
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http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=An_overview_of_
geocoding
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http://www.cdc.gov/dhdsp/maps/gisx/training/module3/files/2_spatial_analyst_modul
e.PDF