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vignettes/adv_groups.Rmd

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+---
+title: "tmap advanced: layer groups (view mode only)"
+output: 
+  bookdown::html_vignette2:
+pkgdown:
+  as_is: true
+template:
+  math-rendering: mathjax
+bibliography: '`r system.file("tmap.bib", package="tmap")`'
+csl: "`r system.file('ieee.csl', package = 'tmap')`"
+editor_options: 
+  chunk_output_type: console
+---
+
+```{r, include = FALSE}
+knitr::opts_chunk$set(
+  fig.width = 8,
+  comment = "#>"
+)
+hook_output <- knitr::knit_hooks$get("output")
+knitr::knit_hooks$set(output = function(x, options) {
+   lines <- options$output.lines
+   if (is.null(lines)) {
+     return(hook_output(x, options))  # pass to default hook
+   }
+   x <- unlist(strsplit(x, "\n"))
+   more <- "..."
+   if (length(lines)==1) {        # first n lines
+     if (length(x) > lines) {
+       # truncate the output, but add ....
+       x <- c(head(x, lines), more)
+     }
+   } else {
+     x <- c(more, x[lines], more)
+   }
+   # paste these lines together
+   x <- paste(c(x, ""), collapse = "\n")
+   hook_output(x, options)
+ })
+
+```
+
+
+```{r, echo = FALSE, message = FALSE}
+library(tmap)
+tmap_options(scale = 0.75)
+```
+
+
+
+## Layer groups
+
+Via the `group` and `group.control` argument in the map layer functions it is possible group layers and (de)select in the leaflet layer control box.
+
+```{r}
+tmap_mode("view")
+tm_shape(NLD_dist) +
+  tm_polygons(
+    fill = "dwelling_value",
+    col = NULL,
+    fill.scale = tm_scale_intervals(values = "-brewer.rd_yl_bu", breaks = c(75, 150, 250, 500, 750, 1000, 1600)),
+    fill.legend = tm_legend("Dwelling value (x 1000)"),
+    group = "District data") +
+tm_shape(NLD_muni) +
+  tm_borders(lwd = 1, col = "black", group = "Municipality borders") +
+tm_title("Select and deselect groups") +
+tm_shape(NLD_prov, name = "Province borders") +
+  tm_borders(lwd = 3) +
+tm_view(set_zoom_limits = c(8,14))
+```
+
+Important is that the plotting order of layers is not affected by the grouping, but specified by the `z` argument. 
+When these are not specified (such as in this example), the order in the plot call is taken (except for `tm_basemap()` which is always drawn at the bottom).
+
+Note that if the `group` argument is not specified, such as in the province layer, the group name is inherited from `tm_shape()`.
+
+
+## Switching between layers
+
+```{r}
+tmap_mode("view")
+tm_shape(NLD_dist) +
+  tm_polygons(
+    fill = "dwelling_value",
+    col = NULL,
+    fill.scale = tm_scale_intervals(values = "-brewer.rd_yl_bu", breaks = c(75, 150, 250, 500, 750, 1000, 1600)),
+    fill.legend = tm_legend("Dwelling value (x 1000)"),
+    group = "District data",
+    group.control = "radio") +
+tm_shape(NLD_muni) +
+  tm_polygons(
+    fill = "dwelling_value",
+    col = NULL,
+    fill.scale = tm_scale_intervals(values = "-brewer.rd_yl_bu", breaks = c(75, 150, 250, 500, 750, 1000, 1600)),
+    fill.legend = tm_legend("Dwelling value (x 1000)"),
+    group = "Municipality data",
+    group.control = "radio") +
+tm_title("Switching between layers") +
+tm_shape(NLD_prov) +
+  tm_borders(lwd = 3, group.control = "none") +
+tm_basemap("OpenStreetMap") +
+tm_view(set_zoom_limits = c(8,14))
+```
+
+
+
+## Zoom-specific map layers
+
+Via `tm_group` it is possible to set the `group.control` and moreover to specify at which zoom levels this group is plotted.
+
+```{r}
+tmap_mode("view")
+tm_shape(NLD_dist) +
+  tm_polygons(
+    fill = "dwelling_value",
+    fill.scale = tm_scale_intervals(values = "-brewer.rd_yl_bu", breaks = c(75, 150, 250, 500, 750, 1000, 1600)),
+    fill.legend = tm_legend("Dwelling value (x 1000)"),
+    group = "District") +
+tm_shape(NLD_muni) +
+  tm_polygons(
+    fill = "dwelling_value",
+    fill.scale = tm_scale_intervals(values = "-brewer.rd_yl_bu", breaks = c(75, 150, 250, 500, 750, 1000, 1600)),
+    fill.legend = tm_legend_hide(),
+    group = "Municipality") +
+tm_borders(group = "District", lwd = 2) +
+tm_title("Zoom in for district level (and out for municipality level)") +
+tm_shape(NLD_prov) +
+  tm_borders(lwd = 3, group.control = "none") +
+tm_group("Municipality", zoom_levels = 8:10) +
+tm_group("District", zoom_levels = 11:14) +
+tm_view(set_zoom_limits = c(8,14))
+```
+