vor_pts <- SpatialPointsDataFrame(cbind(airports$longitude,airports$latitude),airports, match.ID=TRUE)

voronoi <- function(sp) {
    # xtracts polygon data using deldir computation
    vor_desc <- tile.list(deldir(sp@coords[,1], sp@coords[,2]))
    lapply(1:(length(vor_desc)), function(i) {

        # link points to make polygons
        tmp <- cbind(vor_desc[[i]]$x, vor_desc[[i]]$y)
        tmp <- rbind(tmp, tmp[1,])

        # make the polygons
        Polygons(list(Polygon(tmp)), ID=i)

    }) -> vor_polygons

    sp_dat <- sp@data

    rownames(sp_dat) <- sapply(slot(SpatialPolygons(vor_polygons),'polygons'), slot, 'ID')

    SpatialPolygonsDataFrame(SpatialPolygons(vor_polygons),data=sp_dat)
}

vor <- voronoi(vor_pts)
vor_df <- fortify(vor)
states <- map_data("state")
fill <- "state_lines.json"
states <- readOGR("state_lines.json",
                  "OGRGeoJSON", verbose=FALSE)
states <- subset(states, !NAME %in% c("Alaska", "Hawaii", "Puerto Rico"))
dat <- states@data
states <- SpatialPolygonsDataFrame(gSimplify(states, 0.05,topologyPreserve=TRUE),dat, FALSE)