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In our last post mapedit and leaflet.js > 1.0 we discussed remaining tasks for the RConsortium funded project mapedit. mapedit 0.5.0 fixes a couple of lingering issues, but primarily focuses on bringing the power of Leaflet.pm as an alternate editor. Leaflet.draw, the original editor in mapedit provided by leaflet.extras, is a wonderful tool but struggles with snapping and those pesky holes that we commonly face in geospatial tasks. Depending on the task, a user might prefer to continue using Leaflet.draw, so we will maintain full support for both editors. We’ll spend the rest of the post demonstrating where Leaflet.pm excels to help illustrate when you might want to choose editor = "leafpm".

## Install/Update

At a minimum, to follow along with the rest of this post, please update mapedit and install the new standalone package leafpm. While we are it, we highly recommend updating your other geospatial dependencies.

install.packages(c("sf", "leaflet", "leafpm", "mapview", "mapedit"))
# lwgeom is optional but nice when working with holes in leaflet.pm
# install.packages("lwgeom")


## Holes

mapedit now supports holes. Let’s look at a quick example in which we add, edit, and delete holes.

library(sf)
library(leaflet)
library(mapview)
library(mapedit)
library(leafpm)
# make a contrived polygon with holes for testing
outer1 = matrix(c(0,0,10,0,10,10,0,10,0,0),ncol=2, byrow=TRUE)
hole1 = matrix(c(1,1,1,2,2,2,2,1,1,1),ncol=2, byrow=TRUE)
hole2 = matrix(c(5,5,5,6,6,6,6,5,5,5),ncol=2, byrow=TRUE)
outer2 = matrix(c(11,0,11,1,12,1,12,0,11,0),ncol=2, byrow=TRUE)
pts1 = list(outer1, hole1, hole2)
pts2 = list(outer2)
pl1 = st_sf(geom = st_sfc(st_polygon(pts1)))
pl2 = st_sf(geom = st_sfc(st_polygon(pts2)))
mpl = st_sf(geom = st_combine(rbind(pl1, pl2)), crs=4326)
tst = editFeatures(mpl, editor = "leafpm")
# look at our creation
mapview(tst)


Please note that right mouse click deletes vertexes. For a more real world application franconia[5,] from mapview has a hole. Try to edit it with the following code.

library(sf)
library(leaflet)
library(mapview)
library(mapedit)
library(leafpm)
editFeatures(franconia[5,], editor="leafpm")


## Snapping

Leaflet.pm gives us a very pleasant snapping experience, so if you want to snap, set editor = "leafpm" and snap away. Snapping is particular important when drawing/digitizing features from scratch. Here is how it looks with the example from above.

Snapping is enabled by default.

## Fixes For Lingering Issues

### GeoJSON Precision

Robin Lovelace discovered that at leaflet zoom level > 17 we lose coordinate precision. Of course, this is not good enough, so we will prioritize a fix as discussed in issue. Hopefully, this leaflet.js pull request will make this fix fairly straightforward.

I am happy to report that we have found a solution for the loss of precision. Please let us know if you discover any remaining problems.

## Mulitlinestring Editing

Leaflet.js and multilinestrings don’t get along as Tim Appelhans reported in issue. For complete support of sf, mapedit should work with multilinestring, so we have promoted this to issue 62.

We backed into a solution with MULTILINESTRING since Leaflet.pm’s approach fits better with MULTI* features. As an example, let’s edit one of the trails from mapview.

library(sf)
library(leaflet)
library(mapview)
library(mapedit)
library(leafpm)
editFeatures(trails[4,], editor="leafpm")


## Conclusion and Thanks

As of this post we have reached the end of the extremely generous RConsortium funding of mapedit. Although the funding is over, we still expect to actively maintain and improve mapedit. One feature that we had hoped to implement as part of the mapedit toolset was editing of feature attributes. This turned out to be very ambitious, and unfortunately we were not able to implement a satisfactory solution for this feature during the funding period. We plan, however, to develop a solution. Your participation, ideas, and feedback are as vital as ever, so please continue to engage. Thanks to all those who have contributed so far and thanks to all open source contributors in the R and JavaScript communities.