Crime Mapping and Spatial Data Analysis using R

Historically maps have been the primary means to store and communicate spatial data. Objects and their attributes can be readily depicted, and the human eye can quickly discern patterns and outliers in a well-designed map.

In GIS we distinguish between reference and thematic maps. A reference map places the emphasis on the location of spatial objects such as cities, mountains, rivers, parks, etc. You use these maps to orient yourself in space and find out the location of particular places.

Thematic maps, or statistical maps are used to represent the spatial distribution of attributes or statistics. For example, the number of crimes across different neighbourhoods. Our focus in this book is on thematic maps, but often when producing thematic maps you may use a reference map as a backdrop, as a basemap, to help interpretation and to provide context. In this and subsequent chapters we will introduce different types of thematic maps.

Another useful distinction is between static and interactive maps. Your traditional printed road map is an example of a static map, whereas the web application Google maps is an example of an interactive map. In an interactive map you can zoom in and out, you can select and query information about objects in an interactive fashion, etc. In this chapter we introduce the R package ggplot2, which excels at static maps. In other chapters we will introduce other packages, such as leaflet, which is particularly useful for interactive purposes, and the package tmap, in which we can shift our maps between static and interactive mode.