I am trying to perform a spatial join between point data and polygon data.

I have data that indicate the spatial coordinates of an event in my csv file A and have another file, shapefile B, that contains the boundaries of an area as polygons.

  month   longitude latitude lsoa_code                   crime_type
1 2014-09 -1.550626 53.59740 E01007359        Anti-social behaviour
2 2014-09 -1.550626 53.59740 E01007359                 Public order
3 2014-09 -1.865236 53.93678 E01010646        Anti-social behaviour

  code      name                                  altname
0 E05004934 Longfield, New Barn and Southfleet    <NA>
1 E05000448                   Lewisham Central    <NA>
2 E05003149                            Hawcoat    <NA>

I want to join the crime data A to my shapefile B to map the crime events that happen in my area A. Unfortunately I cannot perform an attribute join based code as the code in A refers to different units than the code in B.

I've read a number of tutorials and posts but could not find an answer. I tried:

joined = over(A, B)

and overlay, but did not accomplish what I wanted.

Is there a way to do this join directly or would an intermediate transformation from A to another format be needed?

Conceptually I want to select those points of A that fall into the code areas of B (similar to "join based on spatial location in ArcGIS").

Did someone have this issue and solved it?

migrated from stackoverflow.com Mar 4 '15 at 13:55

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  • Have you looked at point.in.polygon() in package sp? – arvi1000 Mar 3 '15 at 22:53
  • @arvi1000 I have and will try this again. My thought about point.in.polygon was whether this would preserve the variables month and crime_type . Do you know about that? – ben_aaron Mar 3 '15 at 23:23
  • I've tried a bit more with point.in.poly and have finally selected those points that fall into the relevant polygons. Thanks. – ben_aaron Mar 4 '15 at 14:18
  • Then perhaps you should answer your own question with your solution. Remember, good answers are what this site is all about. – SlowLearner Mar 4 '15 at 14:30

The point.in.poly function in the spatialEco package returns a SpatialPointsDataFrame object of the points that intersect an sp polygon object and optionally adds the polygon attributes.

First lets add the require packages and create some example data.

coordinates(meuse) = ~x+y
sr1=Polygons(list(Polygon(cbind(c(180114, 180553, 181127, 181477, 181294, 181007, 180409,
  180162, 180114), c(332349, 332057, 332342, 333250, 333558, 333676,
  332618, 332413, 332349)))),'1')
sr2=Polygons(list(Polygon(cbind(c(180042, 180545, 180553, 180314, 179955, 179142, 179437,
  179524, 179979, 180042), c(332373, 332026, 331426, 330889, 330683,
  331133, 331623, 332152, 332357, 332373)))),'2')
sr3=Polygons(list(Polygon(cbind(c(179110, 179907, 180433, 180712, 180752, 180329, 179875,
  179668, 179572, 179269, 178879, 178600, 178544, 179046, 179110),
  c(331086, 330620, 330494, 330265, 330075, 330233, 330336, 330004,
  329783, 329665, 329720, 329933, 330478, 331062, 331086)))),'3')
sr4=Polygons(list(Polygon(cbind(c(180304, 180403,179632,179420,180304),
  c(332791, 333204, 333635, 333058, 332791)))),'4')
srdf=SpatialPolygonsDataFrame(sr, data.frame(row.names=c('1','2','3','4'), PIDS=1:4, y=runif(4)))

Now, lets take a quick look at the data and plot it.

head(srdf@data)  # polygons
head(meuse@data) # points
points(meuse, pch=20)

Finally, we can intersect the points with the polygons. The results will be a SpatialPointsDataFrame object with, in this case, two extra attributes (PIDS, y) that were contained in the srdf polygon data.

  pts.poly <- point.in.poly(meuse, srdf)

If there is not a unique identification column in the polygon data you could easily add one.

srdf@data$poly.ids <- 1:nrow(srdf) 

Once we have the points and polygons intersected, we can aggregate the points using the unique polygon ID's that were an attribute in the polygon data.

# Number of points in each polygon
tapply(pts.poly@data$lead, pts.poly@data$PIDS, FUN=length)

# Mean lead in each polygon
tapply(pts.poly@data$lead, pts.poly@data$PIDS, FUN=mean)
  • @ arvi1000, yes but sp::point.in.polygon produces a logical. The spatialEco:point.in.poly is a wrapper for over but returns an sp SpatialPointsDataFrame and shortcuts some steps in relating the polygon attributes, much like raster:intersect does for rgeos::gIntersect. – Jeffrey Evans Apr 14 '16 at 16:35
  • sp::point.in.polygon actually returns a numeric value (0=point is outside, 1=inside, 2=on edge, 3=on vertex). Could be the right thing for some circumstances. Thought it was helpful to note here, since this is a top google result for related terms – arvi1000 Apr 14 '16 at 18:02

over() from package sp can be a little confusing but works well. I'm assuming you've already made "A" spatial with coordinates(A) <- ~longitude+latitude:

# Overlay points and extract just the code column: 
a.data <- over(A, B[,"code"])

Instead of a point spatial object, this simply gives you a data frame, with the same no. rows as A, and a single variable "code" from each intersecting polygon from B.

# Add that data back to A:
A$bcode <- a.data$code
  • I have found over() to have issues with points at the vertices of the polygons, although I think this is the easiest solution I have found so far. – JMT2080AD Jul 20 '16 at 19:51
  • What issues have you had? – Simbamangu Jul 21 '16 at 10:48
  • Exclusion. I need to explore it further. I'll pm you some data later today and we can look at it together if your interested. I might be wrong, but I'm pretty sure there are some degeneracies in the algorithm that need to be taken care of, at least for my data. – JMT2080AD Jul 21 '16 at 17:33
  • Nevermind. It must be something with my data. This experimental set works fine. r-fiddle.org/#/fiddle?id=m5sTjE4N&version=1 – JMT2080AD Jul 21 '16 at 22:59
  • 1
    This is a much more straightforward approach than the accepted answer, and does not require installing additional packages other than rgdal. – Bryce Frank Feb 9 '18 at 20:35

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