Make coord_sf() default use projected coords (#4496)

Author: clauswilke

.github/workflows/R-CMD-check.yaml

@@ -1,10 +1,12 @@
-on:
-  push:
-    branches:
-      - master
-  pull_request:
-    branches:
-      - master
+#on:
+#  push:
+#    branches:
+#      - master
+#  pull_request:
+#    branches:
+#      - master
+
+on: [push, pull_request]
 
 name: R-CMD-check
 

NEWS.md

@@ -9,14 +9,13 @@ small selection of feature refinements.
 
 * `coord_sf()` now has an argument `default_crs` that specifies the coordinate
   reference system (CRS) for non-sf layers and scale/coord limits. This argument
-  defaults to the World Geodetic System 1984 (WGS84), which means x and y 
-  positions are interpreted as longitude and latitude. This is a potentially 
-  breaking change for users who use projected coordinates in non-sf layers or in 
-  limits. Setting `default_crs = NULL` recovers the old behavior. Further, 
-  authors of extension packages implementing `stat_sf()`-like functionality are 
-  encouraged to look at the source code of `stat_sf()`'s `compute_group()` 
-  function to see how to provide scale-limit hints to `coord_sf()` 
-  (@clauswilke, #3659).
+  defaults to `NULL`, which means non-sf layers are assumed to be in projected
+  coordinates, as in prior ggplot2 versions. Setting `default_crs = sf::st_crs(4326)`
+  provides a simple way to interpret x and y positions as longitude and latitude,
+  regardless of the CRS used by `coord_sf()`. Authors of extension packages
+  implementing `stat_sf()`-like functionality are encouraged to look at the source
+  code of `stat_sf()`'s `compute_group()` function to see how to provide scale-limit
+  hints to `coord_sf()` (@clauswilke, #3659).
 
 * `ggsave()` now uses ragg to render raster output if ragg is available. It also
   handles custom devices that sets a default unit (e.g. `ragg::agg_png`) 

R/annotation-map.r

@@ -42,6 +42,7 @@ NULL
 #' p +
 #'   coord_sf(
 #'     crs = st_crs(3347),
+#'     default_crs = st_crs(4326),  # data is provided as long-lat
 #'     xlim = c(-84, -76),
 #'     ylim = c(34, 37.2)
 #'   )
@@ -53,7 +54,7 @@ NULL
 #'     data = nc, inherit.aes = FALSE,
 #'     fill = NA, color = "black", size = 0.1
 #'   ) +
-#'   coord_sf(crs = st_crs(3347))
+#'   coord_sf(crs = st_crs(3347), default_crs = st_crs(4326))
 #' }}}
 annotation_map <- function(map, ...) {
   # Get map input into correct form

R/coord-sf.R

@@ -268,7 +268,8 @@ CoordSf <- ggproto("CoordSf", CoordCartesian,
   is_free = function() FALSE,
 
   # for regular geoms (such as geom_path, geom_polygon, etc.), CoordSf is non-linear
-  is_linear = function() FALSE,
+  # if the default_crs option is being used, i.e., not set to NULL
+  is_linear = function(self) is.null(self$get_default_crs()),
 
   distance = function(self, x, y, panel_params) {
     d <- self$backtransform_range(panel_params)
@@ -588,29 +589,26 @@ calc_limits_bbox <- function(method, xlim, ylim, crs, default_crs) {
 #'   be projected before plotting. If not specified, will use the CRS defined
 #'   in the first sf layer of the plot.
 #' @param default_crs The default CRS to be used for non-sf layers (which
-#'   don't carry any CRS information) and scale limits. If not specified, this
-#'   defaults to the World Geodetic System 1984 (WGS84), which means x and y
-#'   positions are interpreted as longitude and latitude, respectively. If
-#'   set to `NULL`, uses the setting for `crs`, which means that then all
+#'   don't carry any CRS information) and scale limits. The default value of
+#'   `NULL` means that the setting for `crs` is used. This implies that all
 #'   non-sf layers and scale limits are assumed to be specified in projected
-#'   coordinates.
+#'   coordinates. A useful alternative setting is `default_crs = sf::st_crs(4326)`,
+#'   which means x and y positions are interpreted as longitude and latitude,
+#'   respectively, in the World Geodetic System 1984 (WGS84).
 #' @param xlim,ylim Limits for the x and y axes. These limits are specified
-#'   in the units of the default CRS. To specify limits in projected coordinates,
-#'   set `default_crs = NULL`. How limit specifications translate into the exact
+#'   in the units of the default CRS. By default, this means projected coordinates
+#'   (`default_crs = NULL`). How limit specifications translate into the exact
 #'   region shown on the plot can be confusing when non-linear or rotated coordinate
-#'   systems are used. First, different methods can be preferable under different
-#'   conditions. See parameter `lims_method` for details. Second, specifying limits
-#'   along only one direction can affect the automatically generated limits along the
-#'   other direction. Therefore, it is best to always specify limits for both x and y.
-#'   Third, specifying limits via position scales or `xlim()`/`ylim()` is strongly
-#'   discouraged, as it can result in data points being dropped from the plot even
-#'   though they would be visible in the final plot region. Finally, specifying limits
-#'   that cross the international date boundary is not possible with WGS84 as the default
-#'   crs. All these issues can be avoided by working in projected coordinates,
-#'   via `default_crs = NULL`, but at the cost of having to provide less intuitive
-#'   numeric values for the limit parameters.
+#'   systems are used as the default crs. First, different methods can be preferable
+#'   under different conditions. See parameter `lims_method` for details. Second,
+#'   specifying limits along only one direction can affect the automatically generated
+#'   limits along the other direction. Therefore, it is best to always specify limits
+#'   for both x and y. Third, specifying limits via position scales or `xlim()`/`ylim()`
+#'   is strongly discouraged, as it can result in data points being dropped from the plot even
+#'   though they would be visible in the final plot region.
 #' @param lims_method Method specifying how scale limits are converted into
-#'   limits on the plot region. For a very non-linear CRS (e.g., a perspective centered
+#'   limits on the plot region. Has no effect when `default_crs = NULL`.
+#'   For a very non-linear CRS (e.g., a perspective centered
 #'   around the North pole), the available methods yield widely differing results, and
 #'   you may want to try various options. Methods currently implemented include `"cross"`
 #'   (the default), `"box"`, `"orthogonal"`, and `"geometry_bbox"`. For method `"cross"`,
@@ -655,7 +653,7 @@ calc_limits_bbox <- function(method, xlim, ylim, crs, default_crs) {
 #' @export
 #' @rdname ggsf
 coord_sf <- function(xlim = NULL, ylim = NULL, expand = TRUE,
-                     crs = NULL, default_crs = sf::st_crs(4326),
+                     crs = NULL, default_crs = NULL,
                      datum = sf::st_crs(4326),
                      label_graticule = waiver(),
                      label_axes = waiver(), lims_method = c("cross", "box", "orthogonal", "geometry_bbox"),

R/geom-sf.R

@@ -24,7 +24,7 @@
 #'
 #' @section CRS:
 #' `coord_sf()` ensures that all layers use a common CRS. You can
-#' either specify it using the `CRS` param, or `coord_sf()` will
+#' either specify it using the `crs` param, or `coord_sf()` will
 #' take it from the first layer that defines a CRS.
 #'
 #' @section Combining sf layers and regular geoms:
@@ -33,21 +33,24 @@
 #' when using these geoms, two problems arise. First, what CRS should be used
 #' for the x and y coordinates used by these non-sf geoms? The CRS applied to
 #' non-sf geoms is set by the `default_crs` parameter, and it defaults to
-#' the World Geodetic System 1984 (WGS84). This means that x and y
-#' positions are interpreted as longitude and latitude, respectively. You can
-#' also specify any other valid CRS as the default CRS for non-sf geoms. Moreover,
-#' if you set `default_crs = NULL`, then positions for non-sf geoms are
-#' interpreted as projected coordinates. This setting allows you complete control
-#' over where exactly items are placed on the plot canvas.
+#' `NULL`, which means positions for non-sf geoms are interpreted as projected
+#' coordinates in the coordinate system set by the `crs` parameter. This setting
+#' allows you complete control over where exactly items are placed on the plot
+#' canvas, but it may require some understanding of how projections work and how
+#' to generate data in projected coordinates. As an alternative, you can set
+#' `default_crs = sf::st_crs(4326)`, the World Geodetic System 1984 (WGS84).
+#' This means that x and y positions are interpreted as longitude and latitude,
+#' respectively. You can also specify any other valid CRS as the default CRS for
+#' non-sf geoms.
 #'
 #' The second problem that arises for non-sf geoms is how straight lines
-#' should be interpreted in projected space. The approach `coord_sf()` takes is
-#' to break straight lines into small pieces (i.e., segmentize them) and
-#' then transform the pieces into projected coordinates. For the default setting
-#' where x and y are interpreted as longitude and latitude, this approach means
-#' that horizontal lines follow the parallels and vertical lines follow the
-#' meridians. If you need a different approach to handling straight lines, then
-#' you should manually segmentize and project coordinates and generate the plot
+#' should be interpreted in projected space when `default_crs` is not set to `NULL`.
+#' The approach `coord_sf()` takes is to break straight lines into small pieces
+#' (i.e., segmentize them) and then transform the pieces into projected coordinates.
+#' For the default setting where x and y are interpreted as longitude and latitude,
+#' this approach means that horizontal lines follow the parallels and vertical lines
+#' follow the meridians. If you need a different approach to handling straight lines,
+#' then you should manually segmentize and project coordinates and generate the plot
 #' in projected coordinates.
 #'
 #' @param show.legend logical. Should this layer be included in the legends?
@@ -78,11 +81,12 @@
 #'   geom_sf(colour = "white") +
 #'   geom_sf(aes(geometry = mid, size = AREA), show.legend = "point")
 #'
-#' # You can also use layers with x and y aesthetics: these are
-#' # assumed to already be in the common CRS.
-#' ggplot(nc) +
+#' # You can also use layers with x and y aesthetics. To have these interpreted
+#' # as longitude/latitude you need to set the default CRS in coord_sf()
+#' ggplot(nc_3857) +
 #'   geom_sf() +
-#'   annotate("point", x = -80, y = 35, colour = "red", size = 4)
+#'   annotate("point", x = -80, y = 35, colour = "red", size = 4) +
+#'   coord_sf(default_crs = sf::st_crs(4326))
 #'
 #' # Thanks to the power of sf, a geom_sf nicely handles varying projections
 #' # setting the aspect ratio correctly.