geom_map

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geom_map creates pure annotation (polygons) that does not affect position scales.

Aesthetics

Other Properties

Similar Geometries

geom_polygon

Description and Details

Using the described geometry, you can insert a geometric object into your data visualization – a map annotation layer. You can find this geometry in the ribbon toolbar tab Layers, under the 2D button.

If you want to use geom_map layer, you need two datasets. One contains geometric data (e.g. coordinates of countries borders) and the other dataset contains the values you want to display in this geometry (e.g. population). So the structure is similar to the shape files (shp and dbf files). Using the Custom Dataset feature we create dataset named crimesm.

This dataset contains statistics about arrests per 100,000 residents for assault, murder and rape in each of the 50 US states in 1973. If we want to display these data on the map, we import into the Stagraph other built-in dataset that contains map coordinates of all US States. The dataset is included in the maps package and we import it through the ribbon button From Terminal – Map – State.

Finally, we have both datasets imported into the program. Information about violent crime rates are in dataset stored in the long format. Dataset contains variables state, variable and value. The map is stored in the states_map dataset and contains coordinates (long & lat variables), group identifier and other region information.

At first, we create a map in the graph using the geom_map geometry layer. We set the data parameter (the dataset that contains the variable you want to Plot), map_id (variable from dataset in the data property that identifies individual states) and the dataset that contains the map itself (map property). For states border, we set the color aesthetic property to gray. Since the coordinate system of plot is not created by the geom_map layer automatically, we have to create them. For this purpose, we used the expand_limits object, which defines axis ranges by the long and lat variables. The final result is shown in the following plot.

In the next step, we Plot the numeric values from the crimesm dataset on displayed map. To display the values, we map the fill aesthetic property to the value variable. We know that this variable contains values of four categories for each state (murder, assault, urbanpop and rape), so we will display them in individual sub-plots using the facet_wrap object. At last, we change the fill scale using the scale_fill_distiller object. Using this object, we setup Diverging – Spectral color palette.

You can also create a similar map using the geom_polyon layer. In this case, however, the variables of both datasets must be merged into one in a long format.