How to read a .MAP file extension in R? - r

Question

Is there a simple way to read a file of .MAP extension in R? I have tried a few options below but had no success. Here is a .MAP file for a reproducible example.
context: For some odd reason, the spatial regionalization used in health planning policies in Brazil is only available in this format. I would like to convert it to geopackage so we can add it to the geobr package.
# none of these options work
mp <- sf::st_read("./se_mapas_2013/se_regsaud.MAP")
mp <- rgdal::readGDAL("./se_mapas_2013/se_regsaud.MAP")
mp <- rgdal::readOGR("./se_mapas_2013/se_regsaud.MAP")
mp <- raster::raster("./se_mapas_2013/se_regsaud.MAP")
mp <- stars::read_stars("./se_mapas_2013/se_regsaud.MAP")
ps. there is a similar question on SO focused on Python, unfortunately unanswered
UPDATE
We have found a publication that uses a custom function that reads the .MAP file. See example below. However, it returns a "polylist" object. Is there a simple way to convert it to a simple feature?
original custom function
read.map = function(filename){
zz=file(filename,"rb")
#
# header of .map
#
versao = readBin(zz,"integer",1,size=2) # 100 = versao 1.00
#Bounding Box
Leste = readBin(zz,"numeric",1,size=4)
Norte = readBin(zz,"numeric",1,size=4)
Oeste = readBin(zz,"numeric",1,size=4)
Sul = readBin(zz,"numeric",1,size=4)
geocodigo = ""
nome = ""
xleg = 0
yleg = 0
sede = FALSE
poli = list()
i = 0
#
# repeat of each object in file
#
repeat{
tipoobj = readBin(zz,"integer",1,size=1) # 0=Poligono, 1=PoligonoComSede, 2=Linha, 3=Ponto
if (length(tipoobj) == 0) break
i = i + 1
Len = readBin(zz,"integer",1,size=1) # length byte da string Pascal
geocodigo[i] = readChar(zz,10)
Len = readBin(zz,"integer",1,size=1) # length byte da string Pascal
nome[i] = substr(readChar(zz,25),1,Len)
xleg[i] = readBin(zz,"numeric",1,size=4)
yleg[i] = readBin(zz,"numeric",1,size=4)
numpontos = readBin(zz,"integer",1,size=2)
sede = sede || (tipoobj = 1)
x=0
y=0
for (j in 1:numpontos){
x[j] = readBin(zz,"numeric",1,size=4)
y[j] = readBin(zz,"numeric",1,size=4)
}
# separate polygons
xInic = x[1]
yInic = y[1]
for (j in 2:numpontos){
if (x[j] == xInic & y[j] == yInic) {x[j]=NA; y[j] = NA}
}
poli[[i]] = c(x,y)
dim(poli[[i]]) = c(numpontos,2)
}
class(poli) = "polylist"
attr(poli,"region.id") = geocodigo
attr(poli,"region.name") = nome
attr(poli,"centroid") = list(x=xleg,y=yleg)
attr(poli,"sede") = sede
attr(poli,"maplim") = list(x=c(Oeste,Leste),y=c(Sul,Norte))
close(zz)
return(poli)
}
using original custom function
mp <- read.map("./se_mapas_2013/se_regsaud.MAP")
class(mp)
>[1] "polylist"
# plot
plot(attributes(mp)$maplim, type='n', asp=1, xlab=NA, ylab=NA)
title('Map')
lapply(mp, polygon, asp=T, col=3)

Answer 1

The problems were: use of readChar with trailing nul bytes - changed to readBin(); 8-bit characters that rawToChar() would not accept (on my UTF-8 system); multiple slivers in some files that needed dropping; and some others. I added the edited read.map() function above to maptools, but with a different name and not exported. So now (with maptools rev 370 from https://r-forge.r-project.org/R/?group_id=943 when build completes):
library(maptools)
o <- maptools:::readMAP2polylist("se_regsaud.MAP")
oo <- maptools:::.makePolylistValid(o)
ooo <- maptools:::.polylist2SpP(oo, tol=.Machine$double.eps^(1/4))
rn <- row.names(ooo)
df <- data.frame(ID=rn, row.names=rn, stringsAsFactors=FALSE)
res <- SpatialPolygonsDataFrame(ooo, data=df)
library(sf)
res_sf <- st_as_sf(res)
res_sf
plot(st_geometry(res_sf))
This approach re-uses the maptools code dating back almost twenty years, with minor edits to handle subsequent changes in reading binary files, and fixing slivers.

Answer 2

EDIT: looks like this doesn't work generally across all files so proper conversion to sf would need a deeper look.
Here's a quick stab at resurrection. It might be incorrect to cumulatively sum to get the multi linestrings, I tested with se_municip.MAP and it only had NAs as the closing row of each ring. If it potentially has non-connected multi-rings (multipolygon) then this approach won't work completely.
x <- read.map("se_municip.MAP")
df <- setNames(as.data.frame(do.call(rbind, x)), c("x", "y"))
df$region.name <- rep(attr(x, "region.name"), unlist(lapply(x, nrow)))
## in case there are multi-rings
df$linestring_id <- cumsum(c(0, diff(is.na(df$x))))
df$polygon_id <- as.integer(factor(df$region.name))
df <- df[!is.na(df$x), ]
sfx <- sfheaders::sf_polygon(df, x = "x", y = "y", linestring_id = "linestring_id", polygon_id = "polygon_id", keep = TRUE)
#sf::st_crs(sfx) <- sf::st_crs(<whatever it is probably 4326>)
plot(sf::st_geometry(sfx), reset = FALSE)
maps::map(add = TRUE)
Interesting that you came across an official version of a forgotten legacy!
(BTW can I publish the data sets in a package?)