# How to split polygons by overlapping feature?

by S Front   Last Updated February 11, 2019 09:22 AM

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.

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#### Answers 1

`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.