Geographic Coordinate

Geographic coordinate uses latitude and longitude to locate a position. Latitude and longitude are just like x-y axes, so you can build all kinds of graphs with them, like Scatterplot and Density Contour Plot.

• In a geographic coordinate, latitude comes first. But it is the north-south direction. Therefore, there is a cross between lat-long and x-y coordinates.

There are also some special graphs for geographic coordinate system, but with controversial performance, like

• Radius Map: use a circle with a radius dependent on an additional variable to represent a dot
• Push Pin Map: use a push pin icon to represent a dot

Implementation

ggmap

Package ggmap can generate real-world maps. It is compatible with ggplot2, so you can easily add layers on top of the base map. Related functions:

• get_stamenmap: get a US map
  • can be zoomed using option bbox, zoom, and the latitude-longitude range of the area
• get_googlemap: get the map of the specified latitude-longitude range from Google map
• ggmap: render the map

sf and tmap

sf and tmap

R Package sf is for reading shape files (.shp). To see the read map, use function st_geometry() and plot the returned object.

R Package tamp is for plotting maps (generated by sf) together with other data. The general workflow is

1. Get the spatial data by reading the shape file using sf
2. Combine spatial data and other data
   • e.g. use left_join()
3. plot the combined data using tmap

Link to original