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Exercise

Spatial joins

For many analysis types you need to link geographies spatially. For example, you want to know how many trees are in each neighborhood but you don't have a neighborhood attribute in the tree data. The best way to do this is with a spatial join using st_join().

Importantly, the st_join() function requires sf data frames as input and will not accept an object that is just sf geometry. You can use the st_sf() function to convert sf geometry objects to an sf data frame (st_sf() is essentially the opposite of st_geometry()).

Instructions
100 XP
  • Plot the beech trees (beech) on top of the neighborhoods (neighborhoods). You will want to plot only the geometry of the neighborhoods.
  • Use class() to see if the beech object has class data.frame or if it's just geometry.
  • Convert the sf geometry object beech to an sf data frame with st_sf().
  • Use class() to confirm that beech now has a class of data.frame (as well as sf).
  • Use st_join() to conduct a spatial join in order to add neighborhood information to the beech object.
  • Use head() to confirm that the new object has neighborhood information -- for example, it should now have neighborhood name (ntaname).
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