Plot multiple shapefiles

Estimated time: 35 minutes

Overview

Questions

• How can I create map compositions with custom legends using ggplot?

Objectives

After completing this episode, participants should be able to…

• Plot multiple vector layers in the same plot.
• Apply custom symbols to spatial objects in a plot.

This episode builds upon the previous episode to work with vector layers in R and explore how to plot multiple vector layers.

Load the data

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To work with vector data in R, we use the sf package. Make sure that it is loaded.

We will continue to work with the three shapefiles that we loaded in the Open and Plot Vector Layers episode.

Plotting Multiple Vector Layers

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So far we learned how to plot information from a single shapefile and do some plot customization. What if we want to create a more complex plot with many shapefiles and unique symbols that need to be represented clearly in a legend?

We will create a plot that combines our leisure locations (point_Delft), municipal boundary (boundary_Delft) and street (lines_Delft) objects. We will also build a custom legend.

To begin, we create a plot with the site boundary as the first layer. Then layer the leisure locations and street data on top in consecutive calls to geom_sf().

R

ggplot() + 
  geom_sf(data = boundary_Delft, 
          fill = "lightgrey", 
          color = "lightgrey"
          ) +
  geom_sf(data = lines_Delft_selection, 
          aes(color = highway), 
          size = 1
          ) +
  geom_sf(data = point_Delft) +
  labs(title = "Mobility network of Delft") +
  coord_sf(datum = st_crs(28992))

Next, let’s build a custom legend using the functions scale_color_manual() and scale_fill_manual(). We will use the custom road_colors object created in the previous episode and we will create a new object called leisure_colors to store values of all 15 types of leisure with the rainbow() function.

We also need to customise the shape of the points with the shape aesthetic if we want to determine the colours inside the points. shape = 21 will show the points as circles with a custom fill.

R

point_Delft$leisure <- factor(point_Delft$leisure)
levels(point_Delft$leisure) %>% length()

OUTPUT

[1] 15

R

leisure_colors <- rainbow(15)

ggplot() +
  geom_sf(
    data = boundary_Delft,
    fill = "lightgrey",
    color = "lightgrey"
  ) +
  geom_sf(
    data = lines_Delft_selection,
    aes(color = highway),
    size = 1
  ) +
  geom_sf(
    data = point_Delft,
    aes(fill = leisure),
    shape = 21
  ) +
  scale_color_manual(
    values = road_colors,
    name = "Road Type"
  ) +
  scale_fill_manual(
    values = leisure_colors,
    name = "Lesiure Location"
  ) +
  labs(title = "Mobility network and leisure in Delft") +
  coord_sf(datum = st_crs(28992))

Challenge: Customizing point shapes

What value of shape will display points as squares with custom fills?

Show me the solution

shape = 22 will display points as squares with custom fills. Our previous plot would look like this:

R

ggplot() +
  geom_sf(
    data = boundary_Delft,
    fill = "lightgrey",
    color = "lightgrey"
  ) +
  geom_sf(
    data = lines_Delft_selection,
    aes(color = highway),
    size = 1
  ) +
  geom_sf(
    data = point_Delft,
    aes(fill = leisure),
    shape = 22
  ) +
  scale_color_manual(
    values = road_colors,
    name = "Line Type"
  ) +
  scale_fill_manual(
    values = leisure_colors,
    name = "Leisure Location"
  ) +
  labs(title = "Mobility network and leisure in Delft") +
  coord_sf(datum = st_crs(28992))

We notice that there are quite some playgrounds in the residential parts of Delft, whereas on campus there is a concentration of picnic tables. So that is what our next challenge is about.

Challenge: Visualising multiple layers with a custom legend

Create a map of leisure locations only including playground and picnic_table, with each point coloured by the leisure type. Overlay this layer on top of the lines_Delft layer (the streets). Tell R to plot playgrounds and picnic tables with different shape values. Make sure your plot has a custom legend.

Tip: You can call scale_ functions multiple times for the same layer, for any of the aesthetics used in aes().

Show me the solution

R

leisure_locations_selection <- st_read("data/delft-leisure.shp") %>% 
  filter(leisure %in% c("playground", "picnic_table"))

OUTPUT

Reading layer `delft-leisure' from data source
  `/home/runner/work/r-geospatial-urban/r-geospatial-urban/site/built/data/delft-leisure.shp'
  using driver `ESRI Shapefile'
Simple feature collection with 298 features and 2 fields
Geometry type: POINT
Dimension:     XY
Bounding box:  xmin: 81863.21 ymin: 442621.1 xmax: 87370.15 ymax: 449345.1
Projected CRS: Amersfoort / RD New

R

factor(leisure_locations_selection$leisure) %>% levels()

OUTPUT

[1] "picnic_table" "playground"  

R

blue_orange <- c("cornflowerblue", "darkorange")

R

ggplot() + 
  geom_sf(data = lines_Delft_selection, 
          aes(color = highway)) + 
  geom_sf(data = leisure_locations_selection, 
          aes(fill = leisure, shape = leisure)) + 
  scale_shape_manual(name = "Leisure Type", 
                     values = c(21, 22)) +
  scale_color_manual(name = "Line Type", 
                     values = road_colors) + 
  scale_fill_manual(name = "Leisure Type", 
                    values = blue_orange) + 
  labs(title = "Road network and leisure") + 
  coord_sf(datum = st_crs(28992))

Key Points

• A plot can be a combination of multiple vector layers, each added with a separate call to geom_sf().
• Use the scale_<aesthetic>_manual() functions to customise aesthetics of vector layers such as color, fill, and shape.