title: R Create a Spatial Bubble Plot That Overlays A basemap of the US and other spatial layers as needed
body: <p>I'm trying to produce a nice bubble plot overlaid on top of a basemap of the US (i could import a shapefile if that is preferred but i've been using the R basemaps.</p>
  
  <pre><code>library(ggplot2,sp,raster,maps,mapdata,maptools,ggmap,rgeos)
  myData = data.frame(name=c("Florida","Colorado","california","Harvard","Yellowstone"),
                  lat=c(28.1,39,37,42,44.6), 
                  long=c(-81.6,-105.5,-120,-71,-110),
                  pop=c(280,156,128,118,202))
  </code></pre>
  
  <p>Using this code below, that i adapted from another stack overflow post (<a href="https://stackoverflow.com/questions/23427479/create-bubble-plot-in-r-using-satellite-map">Create bubble plot in R using satellite map</a>), i am able to overlay a bubble plot on a map of the US. However this renders very slowly, the extent is too tight, it is bounded in a box, i'm not able to add other layers to the plot from what i can tell, and the base map is thick and not visually clean.</p>
  
  <pre><code>xy &lt;- myData[,c("long", "lat")]
  nl &lt;- getData('GADM', country="USA", level=1) #raster data, format SpatialPolygonsDataFrame
  nl &lt;- gSimplify(nl, tol=0.01, topologyPreserve=TRUE)
  # coercing the polygon outlines to a SpatialLines object
  spl &lt;- list("sp.lines", as(nl, "SpatialLines"))
  SPDF &lt;- SpatialPointsDataFrame(coords=xy, data=myData)
  coordinates(myData) &lt;- c("lat", "long")
  projection(SPDF)&lt;- "+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs +towgs84=0,0,0"
  coordinates(SPDF)[1:5,] #retrieves spatial coordinates form the dataframe
  bubble(SPDF, "pop", sp.layout=spl, main="This is It!")
  </code></pre>
  
  <p>I can draw a nice basemap using this code. I add points to the map but they are not sized by the pop column in my data. And i can add additional layers to this map. But can i control the size of the points and the symbol itself like i can using a bubble plot?</p>
  
  <pre><code>map(database= "world", ylim=c(45,90), 
      xlim=c(-160,-50), col="grey80", 
      fill=TRUE, projection="gilbert", 
      orientation= c(90,0,225))
  
  coord &lt;- mapproject(myData$lon, myData$lat, proj="gilbert",orientation=c(90, 0, 225))
  points(coord, pch=20, cex=1.2, col="red") 
  </code></pre>
  
  <p>Can anyone please guide me towards the best way to plot a bubble map in R where i can adjust the fill and outline of the symbols in the bubble map, And i can add a clean basemap, that i can a) control the colors of (fill and lines) and b) add additional layers to (for instance another shapefile layer).</p>
  
  <p>Thank you in advance for any advice.</p>