Design mode
tmap offers a special design mode, which can be enabled via tmap_design_mode. Bolow the same map, but the second time with this design mode enabled:
(tm = tm_shape(NLD_muni) +
tm_polygons(fill = "employment_rate",
fill.legend = tm_legend(position = tm_pos_in("left", "top"))) +
tm_compass(position = tm_pos_in("right", "bottom")) +
tm_scalebar(position = tm_pos_in("left", "bottom")))
tmap_design_mode()
#> design.mode: ON
tm
#> ---------------W (in)-H (in)-asp---
#> | device 7.290 8.000 0.911 |
#> | plot area 6.502 7.680 0.847 |
#> | facets area 6.502 7.680 0.847 |
#> | map area 6.502 7.680 0.847 |
#> -----------------------------------
#> Color codings:
#> - light blue outer margins
#> - dark blue buffers around outside cells
#> - light green outside cells
#> - dark green x and ylab cells
#> - pink panels
#> - red margins for outside grid labels
#> - orange margins around maps for grid labels
#> - yellow map area
tm_layout() and tmap options
All options related to the layout of the map, such as background color and margins, can be set via tm_layout.
These options are a subset of all tmap options, which can be set via tmap_options (a stand-alone function) or tm_options, which is supposed to be stacked with the + operator.
Margins
There are three types of margins:
-
inner.marginsare the margins between the shape (i.e. spatial geometries) and the map frame. Vector of four numbers -
meta.marginsare the margins in which map components are drawn. -
outer.marginsare the margins between the plot (maps and components) and the device borders.
Each is specified with a vector of four numbers that correspond to respectively the bottom, left, top, and right margin.The inner.margins are numbers relative to the map frame, and the meta.argins and outer.margins to the graphics device.
An example where both inner and meta margins are specified:
tm_shape(NLD_muni) +
tm_polygons(fill = "employment_rate") +
tm_layout(
inner.margins = c(0.2, 0.2, 0.2, 0.2),
meta.margins = c(0, 0, 0, 0.15))
#> ---------------W (in)-H (in)-asp---
#> | device 7.290 5.000 1.458 |
#> | plot area 5.307 4.800 1.106 |
#> | facets area 4.139 4.800 0.862 |
#> | map area 4.064 4.800 0.847 |
#> -----------------------------------
#> Color codings:
#> - light blue outer margins
#> - dark blue buffers around outside cells
#> - light green outside cells
#> - dark green x and ylab cells
#> - pink panels
#> - red margins for outside grid labels
#> - orange margins around maps for grid labels
#> - yellow map area
Via the inner margins, the space between the borders of the Netherlands and the map frame is set to 0.2 in each direction. This value is relative to the width (for the left and right-handside margin) and height (top and bottom margin). In other words, the bounding box of the Netherlands occupies 60 percent of the horizontal space and 60 percent of the vertical space of the map frame, shown as the yellow box in design mode.
The meta margins is the space dedicated for map components that are outside the map (see vignette about component positions. The value of the right-handside meta margin 0.15 in this example means that 15 percent of the total device width is used for the ouside components (in this example the legend), shown in the green box. If not specified, for single maps this is calculated automatically, using the other margins and the map component sizes. If there are no outside map components, meta.margins is set to c(0, 0, 0, 0). For complex maps (e.g. facetted maps) it is set to 0.4 for each side in which map components are placed.
The outer margins can also be specified. By default these are 0.02 in each dimension. This is shown in the light blue area. Note that the left and right-handside margin are larger. This is caused by a mismatch between the plot (map and outside components) and the device. Because the aspect ratio of the device is larger (more landscape) than that of the map and components, the ‘excess’ margin is also added to the outer margins. It is also possible to add this ‘excess’ margin to the inner margins by setting asp = 0. This is explained in the next section.
Aspect ratio
The aspect of the map frame can be set via the option asp. If so, the inner margins will be adjusted automatically. The aspect ratio is defined by width / height, so a value one mean square:
tm_shape(NLD_muni) +
tm_polygons(fill = "employment_rate") +
tm_title("Square map") +
tm_layout(asp = 1)
#> ---------------W (in)-H (in)-asp---
#> | device 7.29 5.00 1.46 |
#> | plot area 5.53 4.80 1.15 |
#> | facets area 4.50 4.50 1.00 |
#> | map area 4.43 4.43 1.00 |
#> --------------------------------
#> Color codings:
#> - light blue outer margins
#> - dark blue buffers around outside cells
#> - light green outside cells
#> - dark green x and ylab cells
#> - pink panels
#> - red margins for outside grid labels
#> - orange margins around maps for grid labels
#> - yellow map area
A special case is the value 0. Then the aspect ratio of the graphics device is taken. Now the ‘excess’ margin (see previous section) is added to the inner margins, and the outer margins are unchanged. Hence, a useful trick is to set both asp and outer.margins to 0:
tm_shape(NLD_muni) +
tm_polygons(fill = "employment_rate") +
tm_layout(outer.margins = c(0, 0, 0, 0),
asp = 0)
#> ---------------W (in)-H (in)-asp---
#> | device 7.29 5.00 1.46 |
#> | plot area 7.29 5.00 1.46 |
#> | facets area 6.26 5.00 1.25 |
#> | map area 6.18 5.00 1.24 |
#> --------------------------------
#> Color codings:
#> - light blue outer margins
#> - dark blue buffers around outside cells
#> - light green outside cells
#> - dark green x and ylab cells
#> - pink panels
#> - red margins for outside grid labels
#> - orange margins around maps for grid labels
#> - yellow map area
The result is that the map frame (if drawn) corresponds to the borders of the graphics device.