Marks

The cartographic representations produced with the geoviz package are based on specific graphical marks defined within the package. These marks are used in the various rendering functions, but they can also be used directly on their own. We have already seen the viz_path mark, which allows spatial dataframes to be displayed. But there are other types as well. Let’s start with the viz_circle mark to understand the principle.

Circle

As the name implies, the viz_circle function is used to draw circles. The r attribute allows to define the radius. To customize the style, you can use svg attributes with camelcase notation such as stroke, fill, strokeWidth, fillOpacity, strokeDasharray…

1 - SVG position

You can use this mark to add a circle to the map, giving its x,y position with the pos attribute. In this case, the circle is static, it doesn’t move when you zoom in on the map.

viz_create(projection = "equalEarth", zoomable = T) |>
  viz_path(datum = world, fill = "#CCC", fillOpacity = 0.5) |>
  viz_circle(r = 10, pos = c(300, 100), coords = "svg", fill = "#38896F") |>
  viz_render()

2 - Geographic position

You can also give a geographic position in latitude and longitude. In this case, set coords to "geo". In this case, the circle move when you zoom in on the map.

viz_create(projection = "equalEarth", zoomable = T) |>
  viz_path(datum = world, fill = "#CCC", fillOpacity = 0.5) |>
  viz_circle(r = 10, pos = c(72.88, 19.07), coords = "geo", fill = "#38896F") |>
  viz_render()

3 - based on a spatial dataframe

The mark circle can also be used to draw circles from a spatial dataframe, using the data attribute instead of the pos attribute. If the input data contains points, the circles are mapped onto these points. In the case of polygons or multipolygons, the circle is drawn at the center of the largest polygon.

viz_create(projection = "equalEarth", zoomable = T) |>
  viz_path(datum = world, fill = "#CCC", fillOpacity = 0.5) |>
  viz_circle(r = 5, data = world, fill = "#38896F") |>
  viz_render()

4 - Proportionnal symbols

To vary the the area of the circles proportionally to an absolute quantitative data, all you have to do is specify the variable name in the r attribute. Moreover, the k parameter lets you define the radius of the largest circle. The fixmax parameter allows you to set this radius to a specific value. This one is very useful for comparing different maps or for time evolution.

viz_create(projection = "equalEarth", zoomable = T) |>
  viz_path(datum = world, fill = "#CCC", fillOpacity = 0.5) |>
  viz_circle(r = "pop", k = 30, data = world, fill = "#38896F") |>
  viz_render()

Text

It’s exactly the same principle for text. You can position text using SVG coordinates, geographic coordinates, or from a spatial dataframe.

viz_create(projection = "equalEarth", zoomable = T) |>
  viz_path(datum = world, fill = "#CCC", fillOpacity = 0.5) |>
  viz_text(text = "Hello Geoviz", fontSize = 30, fontWeight = "bold", coords = "svg", pos = c(300, 100), fill = "#38896F") |>
  viz_render()

viz_create(projection = "equalEarth", zoomable = T) |>
  viz_path(datum = world, fill = "#CCC", fillOpacity = 0.5) |>
  viz_text(data = world, text = "ISO3", fill = "#38896F") |>
  viz_render()

Square

The viz_square function mark is used to draw squares. The side attribute allows to define the size of the square (instead of r for circles). Otherwise, the function works exactly the same.

For example:

viz_create(projection = "equalEarth", zoomable = T) |>
  viz_path(datum = world, fill = "#CCC", fillOpacity = 0.5) |>
  viz_square(data = world, side = 5, angle = 45, fill = "#38896F") |>
  viz_render()

Spike

The viz_spike function allows to create spikes. You can vary the width, height and straight parameters.

For example:

afr <- world[world$region == "Africa",]
viz_create(projection = "mercator", zoomable = T) |>
  viz_path(datum = afr, fill = "#CCC", fillOpacity = 0.5) |>
  viz_spike(data = afr, height = "pop", k = 200, fill = "#38896F", stroke = "#38896F") |>
  viz_render()

Half-circle

The viz_halfcircle function is used to draw half-circles. The r attribute allows to define the radius.

afr <- world[world$region == "Africa",]
viz_create(projection = "mercator", zoomable = T) |>
  viz_path(datum = afr, fill = "#CCC", fillOpacity = 0.5) |>
  viz_halfcircle(data = afr, r = 30, fill = "#38896F") |>
  viz_render()

Symbol

As the name implies, the function viz_symbol is used to draw symbols. The r attribute allows to define the size of the symbol (radius of the circle including the symbol).

afr <- world[world$region == "Africa",]
viz_create(projection = "mercator", zoomable = T) |>
  viz_path(datum = afr, fill = "#CCC", fillOpacity = 0.5) |>
  viz_symbol(data = afr, r = "gdp", k = 60, fill = "#38896F", symbol = "fist") |>
  viz_render()

It’s very powerfull

With marks and legend, yout can custom your maps as you want. Here find a mushroom map.

afr <- world[world$region == "Africa",]
viz_create(projection = "mercator", zoomable = T) |>
  viz_path(datum = afr, fill = "#CCC", fillOpacity = 0.5) |>
  viz_halfcircle(data = afr, r = "gdp", fill = "#F13C47", fillOpacity = 0.7, tip = "GDP: $gdp") |>
  viz_halfcircle(data = afr, r = "pop", fill = "#319ABF", fillOpacity = 0.7, angle = 180, tip = "POP: $pop") |>
  viz_leg_mushrooms(top_data = afr$gdp, bottom_data = afr$pop, 
                    title = "Inequalities\nin Africa",
                    top_title = "Wealth", bottom_title = "Population",
                    frame = TRUE, pos = c(20, 200)
                    ) |>
  viz_render()

Nicolas Lambert