point2poly_tess {SUNGEO}

Point-to-polygon interpolation, tessellation method

Description

Function for interpolating values from a source point layer to a destination polygon layer, using Voronoi tessellation and area/population weights.

Usage

point2poly_tess(
  pointz,
  polyz,
  poly_id,
  char_methodz = "aw",
  methodz = "aw",
  pop_raster = NULL,
  varz = NULL,
  pycno_varz = NULL,
  char_varz = NULL,
  char_assign = "biggest_overlap",
  funz = function(x, w) {
     stats::weighted.mean(x, w, na.rm = TRUE)
 },
  return_tess = FALSE,
  seed = 1
)

Arguments

pointz

Source points layer. sf object.

polyz

Destination polygon layer. Must have identical CRS to pointz. sf object.

poly_id

Name of unique ID column for destination polygon layer. Character string.

char_methodz

Interpolation method(s) for character strings. Could be either of "aw" (areal weighting, default) or "pw" (population weighting). See "details". Character string.

methodz

Interpolation method(s) for numeric covariates. Could be either of "aw" (areal weighting, default) and/or "pw" (population weighting). See "details". Character string or vector of character strings.

pop_raster

Population raster to be used for population weighting, Must be supplied if methodz="pw". Must have identical CRS to poly_from. raster or SpatRaster object.

varz

Names of numeric variable(s) to be interpolated from source polygon layer to destination polygons. Character string or list of character strings.

pycno_varz

Names of spatially extensive numeric variables for which the pycnophylactic (mass-preserving) property should be preserved. Character string or vector of character strings.

char_varz

Names of character string variables to be interpolated from source polygon layer to destination polygons. Character string or vector of character strings.

char_assign

Assignment rule to be used for variables specified in char_varz. Could be either "biggest_overlap" (default) or "all_overlap". See "details". Character string or vector of character strings.

funz

Aggregation function to be applied to variables specified in varz. Must take as an input a numeric vector x and vector of weights w. Function or list of functions.

return_tess

Return Voronoi polygons, in addition to destinaton polygon layer? Default is FALSE. Logical.

seed

Seed for generation of random numbers. Default is 1. Numeric.

Details

This function interpolates point data to polygons with a two-step process. In the first step (tessellation), each point is assigned a Voronoi cell, drawn such that (a) the distance from its borders to the focal point is less than or equal to the distance to any other point, and (b) no gaps between cells remain. The second step (interpolation) performs a polygon-in-polygon interpolation, using the Voronoi cells as source polygons.

Currently supported integration methods in the second step (methodz) include:

• Areal weighting ("aw"). Values from poly_from weighted in proportion to relative area of spatial overlap between source features and geometries of poly_to.

• Population weighting ("pw"). Values from poly_from weighted in proportion to relative population sizes in areas of spatial overlap between source features and geometries of poly_to. This routine uses a third layer (supplied in pop_raster) to calculate the weights.

When a list of variables are supplied and one methods argument specified, then the chosen method will be applied to all variables.

When a list of of variables are supplied and multiple methods arguments specified, then weighting methods will be applied in a pairwise order. For example, specifying varz = list(c("to1","pvs1_margin"), c("vv1")) and methodz = c('aw', 'pw') will apply areal weighting to the the first set of variables (to1 and pvs1_margin) and population weighing to the second set (vv1).

Interpolation procedures are handled somewhat differently for numeric and character string variables. For numeric variables supplied in varz, "aw" and/or "pw" weights are passed to the function specified in funz. If different sets of numeric variables are to be aggregated with different functions, both varz and funz should be specified as lists (see examples below).

For character string (and any other) variables supplied in char_varz, "aw" and/or "pw" weights are passed to the assignment rule(s) specified in char_assign. Note that the char_varz argument may include numerical variables, but varz cannot include character string variables.

Currently supported assignment rules for character strings (char_assign) include:

• "biggest_overlap". For each variable in char_varz, the features in poly_to are assigned a single value from overlapping poly_from features, corresponding to the intersection with largest area and/or population weight.

• "all_overlap". For each variable in char_varz, the features in poly_to are assigned all values from overlapping poly_from features, ranked by area and/or population weights (largest-to-smallest) of intersections.

It is possible to pass multiple arguments to char_assign (e.g. char_assign=c("biggest_overlap","all_overlap")), in which case the function will calculate both, and append the resulting columns to the output.

Value

If return_tess=FALSE, returns a sf polygon object, with variables from pointz interpolated to the geometries of polyz.

If return_tess=TRUE, returns a list, containing

• "result". The destination polygon layer. sf object.

• "tess". The (intermediate) Voronoi tessellation polygon layer. sf object.

Examples

# Interpolation of a single variable, with area weights
## Not run: 
data(hex_05_deu)
data(clea_deu2009_pt)
out_1 <- point2poly_tess(pointz = clea_deu2009_pt,
                             polyz = hex_05_deu,
                             poly_id = "HEX_ID",
                             varz = "to1")
plot(out_1["to1_aw"])

## End(Not run)

# Extract and inspect tessellation polygons
## Not run: 
out_2 <- point2poly_tess(pointz = clea_deu2009_pt,
                             polyz = hex_05_deu,
                             poly_id = "HEX_ID",
                             varz = "to1",
                             return_tess = TRUE)
plot(out_2$tess["to1"])
plot(out_2$result["to1_aw"])

## End(Not run)

# Interpolation of multiple variables, with area and population weights
## Not run: 
data(gpw4_deu2010)
out_3 <- point2poly_tess(pointz = clea_deu2009_pt,
                         polyz = hex_05_deu,
                         poly_id = "HEX_ID",
                         methodz = c("aw","pw"),
                         varz = list(
                           c("to1","pvs1_margin"),
                           c("vv1")
                         ),
                         pycno_varz = "vv1",
                         funz = list(
                           function(x,w){stats::weighted.mean(x,w)},
                           function(x,w){sum(x*w)}
                           ),
                         char_varz = c("incumb_pty_n","win1_pty_n"),
                         pop_raster = gpw4_deu2010)
plot(out_3["vv1_pw"])

## End(Not run)