# cartography

#### Timothée Giraud, Nicolas Lambert

#### 2023-09-14

# 1 Introduction

The aim of `cartography` is to obtain thematic maps with the visual quality of those build with a classical mapping or GIS software.

Users of the package could belong to one of two categories: cartographers willing to use R or R users willing to create maps. Therefore, its functions have to be intuitive to cartographers and ensure compatibility with common R workflows.

`cartography` uses `sf` or `sp` objects to produce `base` graphics. As most of the internals of the package relies on `sf` functionalities, the preferred format for spatial objects is `sf`.

# 2 Features

`cartography`’s functions can be classified in the following categories :

- Symbology
  Each function focuses on a single cartographic representation (e.g. proportional symbols or choropleth representation) and displays it on a georeferenced plot. This solution allows to consider each representation as a layer and to overlay multiple representations on a same map.
  Each function has two main arguments that are:

  - `x`, a spatial object (preferably an `sf` object),
  - `var`, the name of a variable to map.

  `sp` objects are handled through the `spdf` argument if the variable is contained within the `Spatial*DataFrame` and through `spdf`, `spdfid`, `df`, `dfid` if the variable is in a separate `data.frame` that needs to be joined to the `Spatial*DataFrame`.

  Many parameters are available to fine tune the cartographic representations. These parameters are the common ones found in GIS and automatic cartography tools (e.g. classification and color palettes used in choropleth maps, symbols sizes used in proportional symbols maps…).

- Transformations
  A set of functions is dedicated to the creation or transformation of spatial objects (e.g. borders extraction, grid or links creation). These functions are provided to ease the creation of some more advanced maps that usually need geo-processing.

- Map Layout
  Along with the cartographic functions, some other functions are dedicated to layout design (e.g. customizable scale bar, north arrow, title, sources or author information…).

- Color Palettes
  16 original color palettes are shipped within the package. Those palettes can be customized and combined.

- Legends
  Legends are displayed by default along cartographic layers but more parameters are available through `legend*()` functions.

- Classification
  `getBreaks()` give access to most of the classification methods used for data binning.

# 3 Examples of thematic maps

## 3.1 Proportional Symbols

`propSymbolsLayer()` displays symbols with areas proportional to a quantitative variable (stocks). Several symbols are available (circles, squares, bars). The `inches` argument is used to customize the symbols sizes.

    library(sf)
    library(cartography)
    # path to the geopackage file embedded in cartography
    path_to_gpkg <- system.file("gpkg/mtq.gpkg", package="cartography")
    # import to an sf object
    mtq <- st_read(dsn = path_to_gpkg, quiet = TRUE)
    # plot municipalities (only borders are plotted)
    plot(st_geometry(mtq), col = "grey80", border = "grey")
    # plot population
    propSymbolsLayer(
      x = mtq,
      var = "POP",
      inches = 0.25,
      col = "brown4",
      legend.pos = "topright",
      legend.title.txt = "Total population"
    )
    # layout
    layoutLayer(title = "Population Distribution in Martinique",
                sources = "Sources: Insee and IGN, 2018",
                author = paste0("cartography ", packageVersion("cartography")),
                frame = FALSE, north = FALSE, tabtitle = TRUE)
    # north arrow
    north(pos = "topleft")

## 3.2 Choropleth Map

In choropleth maps, areas are shaded according to the variation of a quantitative variable. They are used to represent ratios or indices.

`choroLayer()` displays choropleth maps . Arguments `nclass`, `method` and `breaks` allow to customize the variable classification. `getBreaks()` allow to classify outside of the function itself. Colors palettes are defined with `col` and a set of colors can be created with `carto.pal()` (see also `display.carto.all()`).

    library(sf)
    library(cartography)
    # path to the geopackage file embedded in cartography
    path_to_gpkg <- system.file("gpkg/mtq.gpkg", package="cartography")
    # import to an sf object
    mtq <- st_read(dsn = path_to_gpkg, quiet = TRUE)
    # population density (inhab./km2) using sf::st_area()
    mtq$POPDENS <- 1e6 * mtq$POP / st_area(mtq)
    # plot municipalities (only the backgroung color is plotted)
    plot(st_geometry(mtq), col = NA, border = NA, bg = "#aadaff")
    # plot population density
    choroLayer(
      x = mtq,
      var = "POPDENS",
      method = "geom",
      nclass=5,
      col = carto.pal(pal1 = "sand.pal", n1 = 5),
      border = "white",
      lwd = 0.5,
      legend.pos = "topright",
      legend.title.txt = "Population Density\n(people per km2)",
      add = TRUE
    )
    # layout
    layoutLayer(title = "Population Distribution in Martinique",
                sources = "Sources: Insee and IGN, 2018",
                author = paste0("cartography ", packageVersion("cartography")),
                frame = FALSE, north = FALSE, tabtitle = TRUE, theme= "sand.pal")
    # north arrow
    north(pos = "topleft")

## 3.3 Colored Pencil and Typologies Map

`getPencilLayer()` transforms POLYGONS or MULTIPOLYGONS in MULTILINESTRINGS. This function creates a layer that mimicks a pencil hand-drawing.

`typoLayer()` displays a typology map of a qualitative variable. `legend.values.order` is used to set the modalities order in the legend.

    library(sf)
    library(cartography)
    # path to the geopackage file embedded in cartography
    path_to_gpkg <- system.file("gpkg/mtq.gpkg", package="cartography")
    # import to an sf object
    mtq <- st_read(dsn = path_to_gpkg, quiet = TRUE)
    # transform municipality multipolygons to (multi)linestrings
    mtq_pencil <- getPencilLayer(
      x = mtq,
      size = 400,
      lefthanded = F
    )
    # plot municipalities (only the backgroung color is plotted)
    plot(st_geometry(mtq), col = "white", border = NA, bg = "lightblue1")
    # plot administrative status
    typoLayer(
      x = mtq_pencil,
      var="STATUS",
      col = c("aquamarine4", "yellow3","wheat"),
      lwd = .7,
      legend.values.order = c("Prefecture",
                              "Sub-prefecture",
                              "Simple municipality"),
      legend.pos = "topright",
      legend.title.txt = "",
      add = TRUE
    )
    #  plot municipalities
    plot(st_geometry(mtq), lwd = 0.5, border = "grey20", add = TRUE, lty = 3)
    # labels for a few  municipalities
    labelLayer(x = mtq[mtq$STATUS != "Simple municipality",], txt = "LIBGEO",
               cex = 0.9, halo = TRUE, r = 0.15)
    # title, source, author
    layoutLayer(title = "Administrative Status",
                sources = "Sources: Insee and IGN, 2018",
                author = paste0("cartography ", packageVersion("cartography")),
                north = FALSE, tabtitle = TRUE, postitle = "right",
                col = "white", coltitle = "black")
    # north arrow
    north(pos = "topleft")

## 3.4 Proportional Symbols and Choropleth Map

`propSymbolsChoroLayer()` creates a map of symbols that are proportional to values of a first variable and colored to reflect the classification of a second variable. A combination of `propSymbolsLayer()` and `choroLayer()` arguments is used.

    library(sf)
    library(cartography)
    # path to the geopackage file embedded in cartography
    path_to_gpkg <- system.file("gpkg/mtq.gpkg", package="cartography")
    # import to an sf object
    mtq <- st_read(dsn = path_to_gpkg, quiet = TRUE)
    # Plot the municipalities
    plot(st_geometry(mtq), col="darkseagreen3", border="darkseagreen4",
         bg = "lightblue1", lwd = 0.5)
    # Plot symbols with choropleth coloration
    propSymbolsChoroLayer(
      x = mtq,
      var = "POP",
      border = "grey50",
      lwd = 1,
      legend.var.pos = "topright",
      legend.var.title.txt = "Population",
      var2 = "MED",
      method = "equal",
      nclass = 4,
      col = carto.pal(pal1 = "sand.pal", n1 = 4),
      legend.var2.values.rnd = -2,
      legend.var2.pos = "left",
      legend.var2.title.txt = "Median\nIncome\n(in euros)"
    )
    # layout
    layoutLayer(title="Population & Wealth in Martinique, 2015",
                author = "cartography 2.1.3",
                sources = "Sources: Insee and IGN, 2018",
                scale = 5, tabtitle = TRUE, frame = FALSE)
    # north arrow
    north(pos = "topleft")

## 3.5 Proportional Symbols and Typology Map

`propSymbolsTypoLayer()` creates a map of symbols that are proportional to values of a first variable and colored to reflect the modalities of a second qualitatice variable. A combination of `propSymbolsLayer()` and `typoLayer()` arguments is used.

    library(sf)
    library(cartography)
    # path to the geopackage file embedded in cartography
    path_to_gpkg <- system.file("gpkg/mtq.gpkg", package="cartography")
    # import to an sf object
    mtq <- st_read(dsn = path_to_gpkg, quiet = TRUE)
    # Plot the municipalities
    plot(st_geometry(mtq), col="#f2efe9", border="#b38e43", bg = "#aad3df",
         lwd = 0.5)
    # Plot symbols with choropleth coloration
    propSymbolsTypoLayer(
      x = mtq,
      var = "POP",
      inches = 0.5,
      symbols = "square",
      border = "white",
      lwd = .5,
      legend.var.pos = "topright",
      legend.var.title.txt = "Population",
      var2 = "STATUS",
      legend.var2.values.order = c("Prefecture", "Sub-prefecture",
                                   "Simple municipality"),
      col = carto.pal(pal1 = "multi.pal", n1 = 3),
      legend.var2.pos = c(692000, 1607000),
      legend.var2.title.txt = "Administrative\nStatus"
    )
    # layout
    layoutLayer(title="Population Distribution in Martinique",
                author = "cartography 2.1.3",
                sources = "Sources: Insee and IGN, 2018",
                scale = 5, tabtitle = TRUE, frame = FALSE)
    # north arrow
    north(pos = "topleft")

## 3.6 Label Map

`labelLayer()` is dedicated to the display of labels on a map. The `overlap = FALSE` argument displays non overlapping labels.

    library(sf)
    library(cartography)
    # path to the geopackage file embedded in cartography
    path_to_gpkg <- system.file("gpkg/mtq.gpkg", package="cartography")
    # import to an sf object
    mtq <- st_read(dsn = path_to_gpkg, quiet = TRUE)
    # plot municipalities
    plot(st_geometry(mtq), col = "#e4e9de", border = "darkseagreen4",
         bg = "lightblue1", lwd = 0.5)
    # plot labels
    labelLayer(
      x = mtq,
      txt = "LIBGEO",
      col= "black",
      cex = 0.7,
      font = 4,
      halo = TRUE,
      bg = "white",
      r = 0.1,
      overlap = FALSE,
      show.lines = FALSE
    )
    # map layout
    layoutLayer(
      title = "Municipalities of Martinique",
      sources = "Sources: Insee and IGN, 2018",
      author = paste0("cartography ", packageVersion("cartography")),
      frame = FALSE,
      north = TRUE,
      tabtitle = TRUE,
      theme = "taupe.pal"
    )

## 3.7 Links Map

`getLinkLayer()` creates a link layer from an `sf` object and a link `data.frame` (long format).
`gradLinkTypoLayer()` displays graduated and colored links.

    library(sf)
    library(cartography)
    # path to the geopackage file embedded in cartography
    path_to_gpkg <- system.file("gpkg/mtq.gpkg", package="cartography")
    # import to an sf object
    mtq <- st_read(dsn = path_to_gpkg, quiet = TRUE)
    # path to the csv file embedded in cartography
    path_to_csv <- system.file("csv/mob.csv", package="cartography")
    # import to a data.frame
    mob <- read.csv(path_to_csv)
    # select workplaces with administrative status = Prefecture or Sub-prefecture
    mob <- mob[mob$sj != "Simple municipality",]
    # create an sf object of links
    mtq_mob <- getLinkLayer(
      x = mtq,
      xid = "INSEE_COM",
      df = mob,
      dfid = c("i","j")
    )
    # set figure background color
    par(bg="grey25")
    # plot municipalities
    plot(st_geometry(mtq), col = "grey13", border = "grey25",
         bg = "grey25", lwd = 0.5)
    # plot graduated links
    gradLinkTypoLayer(
      x = mtq_mob,
      xid = c("i", "j"),
      df = mob,
      dfid = c("i","j"),
      var = "fij",
      breaks = c( 100,  500, 1200, 2500, 4679.0),
      lwd = c(1,4,8,16),
      legend.var.pos = "left",
      legend.var.title.txt = "Nb. of\nCommuters",
      var2 = "sj",
      col = c("grey85", "red4"),
      legend.var2.title.txt = "Workplace",
      legend.var2.pos = "topright"
    )
    # map layout
    layoutLayer(title = "Commuting to Prefectures in Martinique",
                sources = "Sources: Insee and IGN, 2018",
                author = paste0("cartography ", packageVersion("cartography")),
                frame = FALSE, col = "grey25", coltitle = "white",
                tabtitle = TRUE)

## 3.8 Isopleth Map

`smoothLayer()` is deprecated. See the package `potential` instead.

Isopleth maps are based on the assumption that the phenomenon to be represented has a continuous distribution. These maps use a spatial interaction modeling approach which aims to compute indicators based on stock values weighted by distance. It allows a spatial representation of the phenomenon independent from the initial heterogeneity of the territorial division.

## 3.9 Grid Map

The grid-cell method is an option to overcome the arbitrariness and irregularity of an administrative division. It highlights the main trends in the data spatial distribution, splitting the territory in regular blocks. Statistical values are distributed over a regular grid. Cell values are classified and then displayed in areas of color. The principle adopted here is to set each cell’s value with a proportion of the initial geometrical units it overlay (share of intersected area).
`getGridLayer()` builds a regular grid (squares or hexagons) based on a spatial object and computes data that match the grid layer. `choroLayer()` is then used to display the grid on a choropleth map.

    library(sf)
    library(cartography)
    # path to the geopackage file embedded in cartography
    path_to_gpkg <- system.file("gpkg/mtq.gpkg", package="cartography")
    # import to an sf object
    mtq <- st_read(dsn = path_to_gpkg, quiet = TRUE)
    # Create a grid layer, cell size area match the median municipality area
    mygrid <- getGridLayer(
      x = mtq,
      cellsize = median(as.numeric(st_area(mtq))),
      var = "POP",
      type = "hexagonal"
    )
    # Compute population density in people per km2
    mygrid$POPDENS <- 1e6 * mygrid$POP / mygrid$gridarea
    # plot municipalities (only the backgroung color is plotted)
    plot(st_geometry(mtq), col = NA, border = NA, bg = "#deffff")
    # Plot the population density
    choroLayer(x = mygrid, var = "POPDENS", method = "geom", nclass=5,
               col = carto.pal(pal1 = "turquoise.pal", n1 = 5), border = "grey80",
               lwd = 0.5, legend.pos = "bottomleftextra", add = TRUE,
               legend.title.txt = "Population Density\n(people per km2)")
    layoutLayer(title = "Population Distribution in Martinique",
                sources = "Sources: Insee and IGN, 2018",
                author = paste0("cartography ", packageVersion("cartography")),
                frame = FALSE, north = FALSE, tabtitle = TRUE,
                theme = "turquoise.pal")
    # north arrow
    north(pos = "topleft")

## 3.10 Discontinuities Map

Discontinuities maps are based on the variation of a phenomena between contiguous units. This kind of representation focuses spatial breaks. The discontinuity intensity is expressed by the borders’ thickness.
`getBorders()` is used to build a spatial object of borders between units. Each resulting borders contains the ids of its two neighboring units. It is possible to complement these borders with `getOuterBorders()` to compute borders between non-contiguous units (e.g. maritime borders). `discLayer()` computes and displays discontinuities, lines widths reflect the ratio or the absolute difference between values of an indicator in two neighboring units.

    library(sf)
    library(cartography)
    # path to the geopackage file embedded in cartography
    path_to_gpkg <- system.file("gpkg/mtq.gpkg", package="cartography")
    # import to an sf object
    mtq <- st_read(dsn = path_to_gpkg, quiet = TRUE)
    # Compute the population density (inhab./km2) using sf::st_area()
    mtq$POPDENS <- as.numeric(1e6 * mtq$POP / st_area(mtq))
    # Get a SpatialLinesDataFrame of countries borders
    mtq.contig <- getBorders(mtq)
    # plot municipalities (only the backgroung color is plotted)
    plot(st_geometry(mtq), col = NA, border = NA, bg = "lightblue1",
         xlim = c(690574, 745940))
    # Plot the population density with custom breaks
    choroLayer(x = mtq, var = "MED",
               breaks = c(min(mtq$MED), seq(13000, 21000, 2000), max(mtq$MED)),
               col = carto.pal("green.pal", 6),border = "white", lwd = 0.5,
               legend.pos = "topright", legend.title.txt = "Median Income\n(euros)",
               add = TRUE)
    # Plot discontinuities
    discLayer(
      x = mtq.contig,
      df = mtq,
      var = "MED",
      type = "rel",
      method = "geom",
      nclass = 3,
      threshold = 0.4,
      sizemin = 0.7,
      sizemax = 6,
      col = "red4",
      legend.values.rnd = 1,
      legend.title.txt = "Relative\nDiscontinuities",
      legend.pos = "right",
      add = TRUE
    )
    # Layout
    layoutLayer(title = "Wealth Disparities in Martinique, 2015",
                author =  paste0("cartography ", packageVersion("cartography")),
                sources = "Sources: Insee and IGN, 2018",
                frame = FALSE, scale = 5, tabtitle = TRUE,theme = "grey.pal")
    # north arrow
    north(pos = "topleft")

## 3.11 Mapping `sp` Objects

`SpatialPointsDataFrame` and `SpatialPolygonsDataFrame` (from `sp`) are handled through the `spdf` argument if the variable is contained within the `Spatial*DataFrame` and through `spdf`, `spdfid`, `df`, `dfid` if the variable is in a separate `data.frame` that needs to be joined to the `Spatial*DataFrame`.

    library(sp)
    ## The legacy packages maptools, rgdal, and rgeos, underpinning the sp package,
    ## which was just loaded, will retire in October 2023.
    ## Please refer to R-spatial evolution reports for details, especially
    ## https://r-spatial.org/r/2023/05/15/evolution4.html.
    ## It may be desirable to make the sf package available;
    ## package maintainers should consider adding sf to Suggests:.
    ## The sp package is now running under evolution status 2
    ##      (status 2 uses the sf package in place of rgdal)
    library(cartography)
    data("nuts2006")
    # Plot a layer with the extent of the EU28 countries with only a background color
    plot(nuts0.spdf, border = NA, col = NA, bg = "#A6CAE0")
    # Plot non european space
    plot(world.spdf, col  = "#E3DEBF", border = NA, add = TRUE)
    # Plot Nuts2 regions
    plot(nuts0.spdf, col = "grey60",border = "white", lwd = 0.4, add = TRUE)
    # plot the countries population
    propSymbolsLayer(
      spdf = nuts0.spdf,
      df = nuts0.df,
      spdfid = "id",
      dfid = "id",
      var = "pop2008",
      legend.pos = "topright",
      col = "red4",
      border = "white",
      legend.title.txt = "Population"
    )
    # layout
    layoutLayer(title = "Population in Europe, 2008",
                sources = "Data: Eurostat, 2008",
                author =  paste0("cartography ", packageVersion("cartography")),
                scale = 500, frame = TRUE, col = "#688994")
    # north arrow
    north("topleft")

# 4 Datasets

Several datasets are embedded in the package:

- A GeoPackage of Martinique municipalities can be imported via the `st_read()` function of the `sf` package.
  - Sources: Base comparateur de territoires (upload date: 2018-09-25) & ADMIN EXPRESS-COG (2018 edition).
  - Citation: Insee and IGN, 2018
  - Fields:
    - INSEE_COM: Municipality identifier
    - STATUS: Municipality administrative status
    - LIBGEO: Municipality name
    - POP: Total population, 2015
    - MED: Median disposable income adjusted per equivalent household member, in euros, 2015
    - CHOM: Unemployed population, 2015
    - ACT: Active population, 2015
- A csv file of professional mobility flows between Martinique municipalities.
  - Sources: Flux de mobilité - déplacements domicile-lieu de travail (upload date: 2018-08-01)
  - Citation: Insee, 2018
  - Fields:
    - i: Municipality of residence identifier
    - j: Municipality of workplace identifier
    - fij: Flows of workers (employed population, 15 y.o. or more, 2015, only flows > 100)
    - sj: Administrative status of the workplace municipality
- A set of `sp` objects and `data.frame`s on European regions (NUTS) can be loaded in the environment via `data(nuts2006)`. Each layer of this dataset is directly described in the documentation (e.g. `?nuts0.spdf`).