Create a mapview::mapview() method for sfnetwork objects

[agila5]

My favourite approach for interactively exploring spatial data is mapview (and this probably the first R code that @Robinlovelace taught to me while I was in Leeds 🤣). Unfortunately, at the moment there is no way for directly plotting an sfnetwork object with mapview.

# packages
library(sf)
#> Linking to GEOS 3.8.0, GDAL 3.0.4, PROJ 6.3.1
library(tidygraph)
#> 
#> Attaching package: 'tidygraph'
#> The following object is masked from 'package:stats':
#> 
#>     filter
library(sfnetworks)
library(mapview)

# sfn data
sfn_roxel <- as_sfnetwork(roxel)

# plot
mapview(sfn_roxel)
#> Error in (function (classes, fdef, mtable) : unable to find an inherited method for function 'mapView' for signature '"sfnetwork"'

We can always escape the spatial dimension, for example:

mapview(sfn_roxel %>% activate("nodes") %>% st_as_sf(), col.regions = "darkred", legend = NULL) + 
  mapview(sfn_roxel %>% activate("edges") %>% st_as_sf(), color = "black", lwd = 2, legend = NULL)
#> Warning in cbind(`Feature ID` = fid, mat): number of rows of result is not a
#> multiple of vector length (arg 1)

^{Created on 2021-02-15 by the reprex package (v0.3.0)}

but, if you agree, I think that the best solution is to add a new method (here or in mapview package). It's not really that important, but I could work on this addition in the next weeks.

[loreabad6]

Nice idea! I think we could do it the same way as the autoplot.sfnetwork() method (with a dynamic registration of the S3 method), so that we can put mapview on Suggests :)

[agila5]

Thanks! Actually, I think that the mapview code is written using S4. Do you know if we can use the same approach?

[loreabad6]

🤔 mmm I don't think so, as far as I checked on the vctrs package, they don't mention it... let me do some more checks though!

[agila5]

A rough implementation with a toy example:

library(sfnetworks)
library(mapview)

# Setup
setOldClass("sfnetwork")
setMethod(
  f = "mapView",
  signature = "sfnetwork", 
  definition = function(x, draw_lines = TRUE, ...) {
    nodes <- sf::st_as_sf(x, "nodes")
    m1 <- mapview(nodes, ...)
    if (draw_lines) {
      x <- sfnetworks:::explicitize_edges(x)
      edges <- sf::st_as_sf(x, "edges")
      m2 <- mapview(edges, ...)
      m1 + m2
    } else {
      m1
    }
  }
)

# Toy example
sfn <- as_sfnetwork(roxel)
mapview(sfn, legend = NULL)

^{Created on 2023-07-31 with reprex v2.0.2}

I think we can play with it a little bit and then propose it to mapview as a PR (might be easier than adding it to sfnetworks but I'm not sure about that).

[Robinlovelace]

Could be a good one for tmap4? See info on that here: https://github.com/r-tmap/state-of-tmap-2023

[mtennekes]

Thx! A new package is born :-) Please check out https://github.com/r-tmap/tmap.sfnetworks Added you as authors, @agila5 and @Robinlovelace

[Robinlovelace]

Wow impressive! Andrea best equipped to contribute directly to that I guess but happy to take a peak soon...

[agila5]

Hi @mtennekes and thank you very much for your example, it's a great addition! I would be happy to work on that extension after the release of tmap v4 :)

[mtennekes]

Thx @agila5 the main reason to get this working at this stage (and not after tmap4 has been released), is that is serves as a POC for tmap extendability (both regarding spatial object class and new layer functions). I'll continue working on it when needed, that is, from a tmap4 point of view. When it is released, then I'll give the floor to you to work on it. Would you also be happy to be the official maintainer in the future when it is released?

[agila5]

Would you also be happy to be the official maintainer in the future when it is released?

Sure thing!