Geospatial data aggregation: cases & examples

Myeong Lee

0. Getting Ready

This tutorial is based on R.
Sample data is available in the data folder (a sample of Car2Go's location data)
Sample code is availalbe at the .Rmd files.
Currently, there are two sample files available (geo_agg_tutorial.Rmd for geospatial visualization and aggregation; and voronoi_overlay_sample.Rmd for generating Voronoi diagram based on real-world points).

1. Geospatial Points

Loading the data as a dataframe (if lon/lat).
Loading the data as SpatialPointsDataFrame (sp package).

2. Geospatial Polygons

Sources might be GeoJSON, Shapefile, or KML.
Loading the data as SpatialPolygonDataFrame (sp package).
Many boundaries datasets available from Census or city data portals.

3. Basic Geospatial Operations

raster package for intersection, union, and etc.
It's possible to iterate through each polygon in a SpatialPolygonDataFrame.
Example: Aggregation I: Points to Polygons

4. Density-based Viz

Using ggplot and ggmap to visualize frequency using the color gradiation (polygon-based).

5. Generating Polygons

Hexagons (in this example)
Grids
Voronoi diagram

6. Aggregation II: Polygons to Polygons

Intersection and union are still available (raster)
When aggregating different polygon layers, you need to prorate the value of each polygon based on the proportion of the area.