Get Map with Specified Boundary Coordinates

Get Map with specified boundary coordinates

Here is one way. First, you get a map with a certain zoom. Then, you add the lon and lat limit when you draw a figure, which you can do with scale_x_continuous and scale_y_continuous.

library(ggmap)
library(ggplot2)

### Set a range
lat <- c(44.49, 44.5)                
lon <- c(11.33, 11.36)   

### Get a map
map <- get_map(location = c(lon = mean(lon), lat = mean(lat)), zoom = 14,
               maptype = "satellite", source = "google")

### When you draw a figure, you limit lon and lat.      
foo <- ggmap(map)+
       scale_x_continuous(limits = c(11.33, 11.36), expand = c(0, 0)) +
       scale_y_continuous(limits = c(44.49, 44.5), expand = c(0, 0))

foo

Set ggmap boundary based on Latitude and Longitude

You haven't provided us with any of the data, so I'm going to give an example using a dataset in the historydata package. Instead of getting a map based on a location and a zoom, you can get a map based on the bounding box of the latitudes and longitudes in your dataset.

library(historydata)
library(ggmap)
data("catholic_dioceses")

bbox <- make_bbox(catholic_dioceses$long, catholic_dioceses$lat, f = 0.01)
map <- get_map(bbox)

ggmap(map) +
  geom_point(data=catholic_dioceses, aes(x = long, y = lat))

Note that the f = argument to make_bbox() lets you control how much padding there is around your map.

In your case, I think this will work:

library(ggmap)

bbox <- make_bbox(sep$Longitude, sep$Latitude, f = 0.01)
map <- get_map(bbox)

ggmap(map) +
  geom_point(data=sep, aes(x = Longitude, y = Latitude, 
                           color = Percent_SEP12_Assets),
                           size = 9, alpha = 0.6) +
  scale_color_manual(breaks=c("Over 50", "Under 50"), values=c("green","red"))

ggmap plotted with bounding coordinates

What you are trying to do exceeds the boundaries of the map. The maximum positive/negative Latitude on a mercator-style projection is 85.0511... / -85.0511..., because
arctan(sinh(Pi)) * 180 / Pi = 85.0511288.

This code will yield a correct result:

ggmap(map, extent = "panel") + 
scale_x_continuous(limits = c(-170, -30), expand=c(0,0)) +
scale_y_continuous(limits = c(-60, 85), expand=c(0,0))

How to find the boundary points with center and zoom level given?

If you are using the geocoder, it returns a suggested viewort (that is a google.maps.LatLngBounds() object).

See this similar question:
Google Maps API zoom after setcenter

If you only have the center coordinates and the zoom, use them to initialize the map, listen for the bounds_changed event, then use the map.getBounds() function.

All of the above are described in the documentation

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