GIS and mapping
Jakub Nowosad
Robin Lovelace
GIS_workshop2_GIS_Mapping_Nowosad.RmdSlides: https://nowosad.github.io/SIGR2021/workshop1/workshop1_jn.html#1
library(sf)
#> Linking to GEOS 3.9.1, GDAL 3.3.0, PROJ 8.0.1
library(terra)
#> terra version 1.3.4
library(tmap)
library(spData)
library(spDataLarge)Mapping
nz_elev = terra::rast(system.file("raster/nz_elev.tif", package = "spDataLarge"))
plot(nz_elev)
Tmap functions starts with tm_ prefix
tm_borders : outline empty polygons tm_legends : create manual legends tm_layout : overall look of the map (margin, frame, title, background color)
Shapes and layers
raster data
-
tm_raster: elevation, pluviometry, etc. -
tm_rgb: satellite imagery with 3 layers dataset (visible, false colors)
tm_shape(nz_elev) + # data what we want to plot
tm_graticules() + # add graticules, lines in degrees (not working ?)
#tm_grid() + # grid for projected data
tm_raster( # we want to plot the shape as a raster
title = "elevation as asl", # change legend title
style = "cont", # discretization (échelle continue, sans classes)
palette = "-Spectral" # palette spectal inversée
#palette = c("green","blue", "yellow", "red") # palette custom
) +
tm_shape(nz) + # New Zealand vector data
tm_borders(col = "black", # black borders with empty polygons see tm_fill() and tm_polygons()
lwd = 1 ) +
tm_shape(nz_height) +
tm_symbols(size = 0.2, col = 'red', shape = 17) + # chnage point size and colors
tm_add_legend(type = "symbol", col = "red", shape = 17, title = "Highest peaks") +
tm_scale_bar(breaks = c(0,100,200)) +
tm_compass(position = c("right", "top"),
type = "radar",
size = 2) +
tm_credits(text = "N. Roelandt, 2021") +
tm_layout(main.title = "New Zealand topography",
bg.color = "lightblue", # background color #add8e6
inner.margins = c(0.01,0.01,0.01,0.2), # bottom, left, top, right
legend.outside = TRUE,
frame = FALSE)
#> Warning in showSRID(SRS_string, format = "PROJ", multiline = "NO", prefer_proj
#> = prefer_proj): Discarded datum Unknown_based_on_GRS80_ellipsoid in Proj4
#> definition
#> stars object downsampled to 877 by 1140 cells. See tm_shape manual (argument raster.downsample)
library(sf)
nz_4326 = st_transform(nz, 4326)
tm_shape(nz_4326) +
tm_polygons(text.size = 1, breaks = c(0,20))
Explore color palettes in {tmap}
tmaptools::palette_explorer()# needs shiny installed
tm_shape(nz) +
tm_polygons(col = "Median_income",
title = "Median income (USD)",
style = "jenks",
n = 20,
legend.hist = TRUE) +
tm_layout(inner.margins = c(0,0.02,0,0.5)) # ajust margins
tm_shape(nz) +
tm_polygons(col = "Median_income",
title = "Median income (USD)",
style = "jenks",
n = 20,
legend.hist = TRUE,
legend.format = list(digits =1 )) + # mise en forme de la legend
tm_layout(legend.outside = TRUE) # move legend outside the map
Modes
Static map / interactive map
tmap_mode("view") +
tm_shape(nz_elev) + # data what we want to plot
tm_graticules() + # add graticules, lines in degrees (not working ?)
#tm_grid() + # grid for projected data
tm_raster( # we want to plot the shape as a raster
title = "elevation as asl", # change legend title
style = "cont", # discretization (échelle continue, sans classes)
palette = "-Spectral" # palette spectal inversée
#palette = c("green","blue", "yellow", "red") # palette custom
) +
tm_shape(nz) + # New Zealand vector data
tm_borders(col = "black", # black borders with empty polygons see tm_fill() and tm_polygons()
lwd = 1 ) +
tm_shape(nz_height) +
tm_symbols(size = 0.2, col = 'red', shape = 17) + # chnage point size and colors
tm_add_legend(type = "symbol", col = "red", shape = 17, title = "Highest peaks") +
tm_scale_bar(breaks = c(0,100,200)) +
tm_compass(position = c("right", "top"),
type = "radar",
size = 2) +
tm_credits(text = "N. Roelandt, 2021") +
tm_layout(main.title = "New Zealand topography",
bg.color = "lightblue", # background color #add8e6
inner.margins = c(0.01,0.01,0.01,0.2), # bottom, left, top, right
legend.outside = TRUE,
frame = FALSE)
#> tmap mode set to interactive viewing
#> Credits not supported in view mode.
#> Compass not supported in view mode.
#> Warning in showSRID(SRS_string, format = "PROJ", multiline = "NO", prefer_proj
#> = prefer_proj): Discarded datum Unknown_based_on_GRS80_ellipsoid in Proj4
#> definition
#> stars object downsampled to 877 by 1140 cells. See tm_shape manual (argument raster.downsample)
#> Warning: In view mode, scale bar breaks are ignored.
#> Symbol shapes other than circles or icons are not supported in view mode.
#> only legends of type "fill" supported in view modeSaving
my_map = tm_shape(nz_elev) + # data what we want to plot
tm_graticules() + # add graticules, lines in degrees (not working ?)
#tm_grid() + # grid for projected data
tm_raster( # we want to plot the shape as a raster
title = "elevation as asl", # change legend title
style = "cont", # discretization (échelle continue, sans classes)
palette = "-Spectral" # palette spectal inversée
#palette = c("green","blue", "yellow", "red") # palette custom
) +
tm_shape(nz) + # New Zealand vector data
tm_borders(col = "black", # black borders with empty polygons see tm_fill() and tm_polygons()
lwd = 1 ) +
tm_shape(nz_height) +
tm_symbols(size = 0.2, col = 'red', shape = 17) + # change point size and colors
tm_add_legend(type = "symbol", col = "red", shape = 17, title = "Highest peaks") +
tm_scale_bar(breaks = c(0,100,200)) +
tm_compass(position = c("right", "top"),
type = "radar",
size = 2) +
tm_credits(text = "N. Roelandt, 2021") +
tm_layout(main.title = "New Zealand topography",
bg.color = "lightblue", # background color #add8e6
inner.margins = c(0.01,0.01,0.01,0.2), # bottom, left, top, right
legend.outside = TRUE,
frame = FALSE)
my_map
#> Credits not supported in view mode.
#> Compass not supported in view mode.
#> Warning in showSRID(SRS_string, format = "PROJ", multiline = "NO", prefer_proj
#> = prefer_proj): Discarded datum Unknown_based_on_GRS80_ellipsoid in Proj4
#> definition
#> stars object downsampled to 877 by 1140 cells. See tm_shape manual (argument raster.downsample)
#> Warning: In view mode, scale bar breaks are ignored.
#> Symbol shapes other than circles or icons are not supported in view mode.
#> only legends of type "fill" supported in view mode
tmap_save(my_map, filename = "vignettes/images/nz.png", width = 300, height = 800, dpi = 300)
tmap_save(my_map, filename = "vignettes/images/nz.svg")
tmap_save(my_map, filename = "vignettes/images/nz.html")-
tm_: functions to make maps -
tmap_: interact with the whole map
Exercices
library(sf);library(tmap);library(spData);library(dplyr)
#>
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:terra':
#>
#> intersect, src, union
#> The following objects are masked from 'package:stats':
#>
#> filter, lag
#> The following objects are masked from 'package:base':
#>
#> intersect, setdiff, setequal, union
us_states = left_join(us_states, us_states_df, by = c("NAME" = "state"))
us_states2163 = st_transform(us_states, "EPSG:2163")- Run the code above. Create a simple map of the reprojected data for contiguous United States (object us_states2163) with the graticule lines.
us_map = tm_shape(us_states2163) + # data what we want to plot
tm_grid() +
tm_borders(col = "black", lwd =1)
us_map
- Improve the map of the reprojected data for contiguous United States by coloring states based on their median income in 2015 (median_income_15). Improve the legend title. Try different color palettes. Change the width of the borders. Put the legend on the right side of the map.
us_map = us_map +
tm_fill(col = "median_income_15",
title = "2015 median income (in US$)",
palette = )
us_map
- Try different color scale styles. Which one is the best in your opinion?
- Improve the map of the reprojected data for contiguous United States (object us_states2163) further by adding a map title, scale bar, north arrow, and text annotation. Try to improve locations of the map elements.
- Change the tmap mode to “view” and recreate maps from Exercise 4. What are the pros and cons of using static or interactive maps? What are the map’s elements that can exist in static maps, but are not rendered in the interactive maps?
- Save the map from Exercise 4 as a .png, .svg, and .html file. When can different file formats be useful?