How can I divide the multiple overlapping polygons into multiple non-overlapping polygons? Here is an example: I would like to divide the long yellow polygon in the image into 3 polygons based on where it touches the other two.

```
library(spData)
library(sf)
seine_buff_5km = st_buffer(seine, dist = 5000)
tmap_mode("plot")
tm_shape(seine_buff_5km) +
tm_fill( col = "name", alpha =.5) +
tm_shape(seine) +
tm_lines()
```

Of course, I would like to do that for a larger data set with many more polygons. I guess one way to do it is subtract all polygons in an sf object from each other.

`st_intersection`

on a single object will chop it into non-overlapping parts:

```
> bi = st_intersection(seine_buff_5km)
> bi
Simple feature collection with 5 features and 3 fields
geometry type: GEOMETRY
dimension: XY
bbox: xmin: 513345.8 ymin: 6655432 xmax: 884953.8 ymax: 6943863
epsg (SRID): 2154
proj4string: +proj=lcc +lat_1=49 +lat_2=44 +lat_0=46.5 +lon_0=3 +x_0=700000 +y_0=6600000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs
name geometry n.overlaps origins
1 Marne POLYGON ((658951.7 6862882,... 1 1
2 Marne POLYGON ((657550.3 6852588,... 2 1, 2
3 Seine POLYGON ((517155.1 6930721,... 1 2
4 Seine POLYGON ((695195.4 6815345,... 2 2, 3
5 Yonne MULTIPOLYGON (((711168.3 68... 1 3
```

The `origins`

column is a "list-column" that shows which of the original parts form the new part. When plotted in unique colours the five parts look like this:

Note how the green part is treated as a single object because it isn't quite cut into parts by the other polygons.

The fifth row (blue polygon, Yonne), is shown as a MULTIPOLYGON because there is a tiny sliver cut off above the orange polygon.

February 11, 2019 09:04 AM

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