tmap: get started!

knitr::opts_chunk$set(collapse = T, fig.width=6, fig.height=3)
# devtools::install_github("mtennekes/tmaptools")

With the tmap package, thematic maps can be generated with great flexibility. The syntax for creating plots is similar to that of ggplot2, but tailored to maps. This vignette is for those who want to get started with tmap within a couple of minutes. A more detailed description of tmap can be found in an article published in the Journal of Statistical Software (JSS), which describes tmap version 1.11-2. The changes in version 2.0 are described in vignette("tmap-changes-v2").

For more context on R's geographic capabilities there are a number of online resources including the vignettes of the sf package, the website rspatial.org and the online version of the book Geocomputation with R. The Making maps with R chapter of the book provides many more context and abundant code examples of map making with tmap and other packages.

Hello World!

A good place to start is to create a map of the world. After installing tmap, the following lines of code should create the map shown below:

library(tmap)
data("World")

tm_shape(World) +
    tm_polygons("HPI")

The object World is a spatial object of class sf from the sf package; it is a data.frame with a special column that contains a geometry for each row, in this case polygons. In order to plot it in tmap, you first need to specify it with tm_shape. Plotting layers can be added with the + operator, in this case tm_polygons. There are many layer functions in tmap, which can easily be found in the documentation by their tm_ prefix. See also ?'tmap-element'.

Interactive maps

Each map can be plotted as a static image or viewed interactively using "plot" and "view" modes, respectively. The mode can be set with the function tmap_mode, and toggling between the modes can be done with the 'switch' ttm().

tmap_mode("view")

tm_shape(World) +
    tm_polygons("HPI")

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Multiple shapes and layers

A shape is a spatial object (with a class from sf, sp or raster). Multiple shapes and also multiple layers per shape can be plotted:

data(World, metro, rivers, land)

tmap_mode("plot")
tm_shape(land) +
    tm_raster("elevation", palette = terrain.colors(10)) +
tm_shape(World) +
    tm_borders("white", lwd = .5) +
    tm_text("iso_a3", size = "AREA") +
tm_shape(metro) +
    tm_symbols(col = "red", size = "pop2020", scale = .5) +
tm_legend(show = FALSE)

Facets

Facets can be created in three ways:

  1. By assigning multiple variable names to one aesthetic:
tmap_mode("view")
tm_shape(World) +
    tm_polygons(c("HPI", "economy")) +
    tm_facets(sync = TRUE, ncol = 2)

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  1. By splitting the spatial data with the by argument of tm_facets:
tmap_mode("plot")

data(NLD_muni)

NLD_muni$perc_men <- NLD_muni$pop_men / NLD_muni$population * 100

tm_shape(NLD_muni) +
    tm_polygons("perc_men", palette = "RdYlBu") +
    tm_facets(by = "province")
  1. By using the tmap_arrange function:
tmap_mode("plot")

data(NLD_muni)
tm1 <- tm_shape(NLD_muni) + tm_polygons("population", convert2density = TRUE)
tm2 <- tm_shape(NLD_muni) + tm_bubbles(size = "population")

tmap_arrange(tm1, tm2)

Basemaps and overlay tile maps

Tiled basemaps can be added with the layer function tm_basemap. Semi-transparent overlay maps (for example annotation labels) can be added with tm_tiles.

tmap_mode("view")
tm_basemap("Stamen.Watercolor") +
tm_shape(metro) + tm_bubbles(size = "pop2020", col = "red") +
tm_tiles("Stamen.TonerLabels")

See a preview of the available tilemaps. This list is also accessible in R: leaflet::providers.

Options and styles

The functions tm_layout and tm_view are used to specify the map layout and the interactive aspects respectively. These functions can be used in the same way as the layer functions, e.g.

tmap_mode("plot")

tm_shape(World) +
    tm_polygons("HPI") +
tm_layout(bg.color = "skyblue", inner.margins = c(0, .02, .02, .02))

These options, as well as a couple of others, can also be set within with tmap_options, which works in the same way as the base R function options. The main advantage is that these options are set globally, so they do not have to be specified in each map, for the duration of the session.

tmap_options(bg.color = "black", legend.text.color = "white")

tm_shape(World) +
    tm_polygons("HPI", legend.title = "Happy Planet Index")

A style is a certain configuration of the tmap options.

tmap_style("classic")

tm_shape(World) +
    tm_polygons("HPI", legend.title = "Happy Planet Index")
# see what options have been changed
tmap_options_diff()

# reset the options to the default values
tmap_options_reset()

New styles can be created; see ?tmap_options.

Exporting maps

tm <- tm_shape(World) +
    tm_polygons("HPI", legend.title = "Happy Planet Index")

## save an image ("plot" mode)
tmap_save(tm, filename = "world_map.png")

## save as stand-alone HTML file ("view" mode)
tmap_save(tm, filename = "world_map.html")

leaflet and shiny integration

Maps made with tmap can be exported to leaflet with the function tmap_leaflet. Hence, it is possible to make use of leaflet own functionalities. This function is also needed when using tmap in shiny:

# in UI part:
leafletOutput("my_tmap")

# in server part
output$my_tmap = renderLeaflet({
    tm <- tm_shape(World) + tm_polygons("HPI", legend.title = "Happy Planet Index")
    tmap_leaflet(tm)
})

See full tmap - shiny example.

Quick thematic map

Maps can also be made with one function call. This function is qtm:

qtm(World, fill = "HPI", fill.pallete = "RdYlGn")

Tips 'n Tricks

Run:

tmap_tip()


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tmap documentation built on Aug. 10, 2018, 1:07 a.m.