domrussel / nngeo

k-Nearest Neighbor Join for Spatial Data

nngeo

The goal of nngeo is to provide k-nearest neighbor join capabilities for spatial analysis in R.

Installation

CRAN version -

install.packages("nngeo")

GitHub version -

install.packages("devtools")
devtools::install_github("michaeldorman/nngeo")

Usage

Once installed, the library can be loaded as follows.

library(nngeo)
#> Loading required package: sf
#> Linking to GEOS 3.7.1, GDAL 2.4.0, PROJ 5.2.0

Example

The following code section finds the 20-nearest towns for each city using function st_nn.

data(towns)
data(cities)
nn = st_nn(cities, towns, k = 20, progress = FALSE)
#> lon-lat points
nn
#> [[1]]
#>  [1]  70  99  60  15  36  56 193 142  90  82  17  93  44  13  32   9 172
#> [18]  34 103 132
#> 
#> [[2]]
#>  [1] 145 175  57 144  29  55  21  64 138  24 121 146  53 126 160  31  62
#> [18] 187  85  83
#> 
#> [[3]]
#>  [1]  59 179 137 114 141 134  67 152  41 133   6 140  23 166  66   2 189
#> [18]  73 173 147

By default, the result is a sparse list with the neighbor IDs.

The st_nn function can also be used as a geometry predicate function when performing spatial join with sf::st_join.

st_join(cities, towns, join = st_nn, k = 3, progress = FALSE)
#> lon-lat points
#> Simple feature collection with 9 features and 5 fields
#> geometry type:  POINT
#> dimension:      XY
#> bbox:           xmin: 34.78177 ymin: 31.76832 xmax: 35.21371 ymax: 32.79405
#> epsg (SRID):    4326
#> proj4string:    +proj=longlat +datum=WGS84 +no_defs
#>        name.x            name.y country.etc    pop capital
#> 1   Jerusalem         Jerusalem      Israel 731731       1
#> 1.1 Jerusalem Mevasserat Ziyyon      Israel  22470       0
#> 1.2 Jerusalem          Har Adar      Israel   2101       0
#> 2    Tel-Aviv         Ramat Gan      Israel 128583       0
#> 2.1  Tel-Aviv     Tel Aviv-Yafo      Israel 384276       0
#> 2.2  Tel-Aviv        Giv'atayim      Israel  48882       0
#> 3       Haifa             Haifa      Israel 266418       0
#> 3.1     Haifa      Tirat Karmel      Israel  19080       0
#> 3.2     Haifa    Qiryat Motzkin      Israel  39413       0
#>                      geometry
#> 1   POINT (35.21371 31.76832)
#> 1.1 POINT (35.21371 31.76832)
#> 1.2 POINT (35.21371 31.76832)
#> 2    POINT (34.78177 32.0853)
#> 2.1  POINT (34.78177 32.0853)
#> 2.2  POINT (34.78177 32.0853)
#> 3   POINT (34.98957 32.79405)
#> 3.1 POINT (34.98957 32.79405)
#> 3.2 POINT (34.98957 32.79405)

A helper function st_connect can be used to draw lines according to joined feature IDs. This may be useful for visualization or for network analysis.

l = st_connect(cities, towns, ids = nn, progress = FALSE)
#> although coordinates are longitude/latitude, st_nearest_points assumes that they are planar
plot(st_geometry(towns), col = "darkgrey")
plot(st_geometry(cities), col = "red", add = TRUE)
plot(st_geometry(l), add = TRUE)