1-2 Plotting a Basic Map

We can plot vectorial data with tm_shape and tm_polygons

R Code

tm_shape(vancouver_boundaries) + 
  tm_polygons(col="grey", border.col = "white")

tm_shape selects a dataset for plotting

tm_polygons plots any polygons for thtat dataset

Adding Meta-Data

What data is available?

R Code

colnames(vancouver_boundaries)

colnames inspects the columns of our data, either its crs or metadata, e.g. name of neighbourhoods.

R Code

tm_shape(vancouver_boundaries) + 
  tm_polygons(col="name", border.col = "white") +
  tm_legend(outside=TRUE)

Output

Improving Aesthetics

Step-by-step:

First, let’s improve the legend position and add a name to our mape

R Code

# adding meaningfull names
tm_shape(vancouver_boundaries) + 
  tm_polygons(col="name", border.col = "white", title="neighbourhood") +
  tm_legend(outside=TRUE) +
  tm_layout(main.title="City of Vancouver", main.title.position = "left")

Then, let’s improve the color palette. Pastel1 is one of many available palettes. Later we will check what palettes are available

R Code

# changing the colour palette
tm_shape(vancouver_boundaries) + 
  tm_polygons(col="name", border.col = "white", title="neighbourhood", palette = "Pastel1") +
  tm_legend(outside=TRUE) +
  tm_layout(main.title="City of Vancouver", main.title.position = "left")

3 Adding text for neighborhood IDs with tm_text

We ca use tm_text and one of the columns of our data to add extra information to our plot.

R Code

tm_shape(vancouver_boundaries) +
  tm_polygons(col="name", border.col = "white", title="neighbourhood", palette = "Pastel1") +
  tm_text("mapid", just = "center", size = 0.8) +
  tm_legend(outside=TRUE) +
  tm_layout(main.title="City of Vancouver", main.title.position = "left")

Combining Layers

4 Combining polygons and lines with tm_lines

For every dataset that we want to use for plotting, we must append it with tm_shape + some function, e.g. tm_lines, tm_polygons, etc.

R Code

tm_shape(vancouver_boundaries) +
  tm_polygons(col="name", border.col = "white", title="neighbourhood", palette = "Pastel1") +
tm_shape(transit_routes) +
  tm_lines(col="grey70", size=.1) +
  tm_legend(outside=TRUE) +
  tm_layout(main.title="City of Vancouver", main.title.position = "left")

Output

5-6 Combining polygons and dots with tm_dots

R Code

tm_shape(vancouver_boundaries) +
  tm_polygons(col="name", border.col = "white", title="neighbourhood", palette = "Pastel1") +
tm_shape(schools) + 
  tm_dots(col="red", size=.1, shape=18) +
  tm_legend(outside=TRUE) +
  tm_add_legend(
    type = "symbol", 
    shape=c(18), 
    labels=c("Schools"),
    col=c("red")) +  
  tm_layout(main.title="City of Vancouver", main.title.position = "left")

Note that each tm_dots has different shape codes and colors. We must use the same shape and color for our legend.

Available shape codes:

Shape codes

source

Exercise

• Make a map that has the city neighborhoods
• Add schools, libraries and community centres to the map
  • Use different shapes and colors for each
• Change shape, labels and col in tm_add_legend
  • instead of c(18), you can pass a list of values to these parameters, e.g., shape=c(18, 16, 15, 17)

Recap

1 tm_shape defines the dataset for plotting

2 tm_polygons draws polygon shapes based on the dataset provided

3 tm_text adds text in the map

4 tm_lines draws lines based on the dataset provided

5 tm_dots draws dot shapes based on the dataset provided

6 tm_add_legend manually add labels and text for the legend component of the map