title: Facet_wrap over a time factor with ggmap in R
body: <p>I'm trying to generate weekly maps using the same data frame. Here is a sample of my data (den53):</p>
  
  <pre><code>Tower  Tag_ID HourID       count  week    Lon   Lat   DateTime            day
  T01    53     2016-37_6_0  167    2016-37 -94.4 42.81 2016-09-17 00:00:00 Sat
  T01    53     2016-38_3_3  111    2016-38 -94.4 42.81 2016-09-21 03:00:00 Wed
  T06    53     2016-38_2_22 175    2016-38 -94.5 42.82 2016-09-20 22:00:00 Thr
  </code></pre>
  
  <p>And so on. I have 8k+ of data like this. This is telemetry data.  So for each tower I have generated a count per hour of what tags were pinging that area. I'm creating a time lapse map to try and show movement.  Ultimately, I am trying to produce a plot like this one. Older hits are orange, newer are navy.</p>
  
  <p><a href="https://i.stack.imgur.com/p43sm.png" rel="nofollow"><img src="https://i.stack.imgur.com/p43sm.png" alt="Example Map"></a></p>
  
  <p>To generate this plot, I've used the following code:</p>
  
  <pre><code>TMap + #I used ggmap for this. This is a fixed image behind the new information I am trying to plot on top of it. I'm not worried about this code.
  geom_point(aes(x=Lon, y=Lat, size=count, color=as.integer(as.Date(den53$DateTime))), data=den53, alpha=1) +
  scale_colour_gradient(limits=as.integer(as.Date(c(min(den53$DateTime), max(den53$DateTime)))),low="orange", high="navy", name="Time")
  </code></pre>
  
  <p>This is great, but it isn't very informative.  Data is overlapping. I want to look at these maps on a weekly basis.  I think I should be able to do that using the Facet_wrap function. I already have a week column in the datasheet above. However, when I add that function, I get the following error:</p>
  
  <pre><code>TMap + 
  geom_point(aes(x=Lon, y=Lat, size=count, color=as.integer(as.Date(den53$DateTime))), data=den53, alpha=1) +
  scale_colour_gradient(limits=as.integer(as.Date(c(min(den53$DateTime), max(den53$DateTime)))),low="orange", high="navy", name="Time")+
  facet_wrap( ~ week, ncol=2) 
  
  Error: Aesthetics must be either length 1 or the same as the data (210): x, y
  </code></pre>
  
  <p>Any ideas? I can't figure out why facet_wrap isn't working. I thought it may be a gradient v discrete problem, so I tried using a discrete function of time (day) rather than a gradient. no Bueno. I'd really just love to keep my code above mostly the same, just spit out weekly maps.  </p>
  
  <p>thanks!</p>