ggplot annotation in fixed place in the chart
<p>I am plotting the following data into a ggplot bar chart.  </p>

<pre><code>structure(list(MEDIATYPE = c("BACKLIT TOWER", "BILLBOARDS", "BRIDGE PANEL", 
"BUILDING FACADES", "BUS SHELTER", "CANTILIVERS", "CYCLE SHELTER", 
"FOB", "FREE STANDING PANEL", "GANTRIES"), RENTAL = c(197, 278363, 
1423, 26, 35960, 6194, 70, 4845, 27, 9420)), .Names = c("MEDIATYPE", 
"RENTAL"), row.names = c(NA, 10L), class = "data.frame")
</code></pre>

<p>I am using the following code to render the chart.  It is working fine.  However the problem is the yaxis values keeps changing and the annotation at the top of the chart sometimes disappears or in other instances appears in the middle of the chart.  </p>

<pre><code>library(ggplot2)
library(stringr) # str_wrap


ggplot(b, aes(x=reorder(MEDIATYPE,-RENTAL), y=RENTAL, fill=MEDIATYPE)) + geom_bar(stat = "identity", width = 0.8) +
    theme(legend.position = "none") + xlab("MEDIATYPE") + ylab("SPENDS") +
    scale_x_discrete(labels = function(x) str_wrap(x, width = 1)) + 
    theme(axis.text.x = element_text(angle = 90, hjust = 1)) +
    geom_text(aes(label=RENTAL), vjust = 0.5,hjust = 1, angle = 90, colour = "white",size = 3) + 
    ggtitle("MEDIAWISE SPENDS") + 
    theme(plot.title=element_text(size=rel(1.4), lineheight = 1, face = "bold")) +
    theme(axis.text = element_text(size = 8, color = "black")) +
    theme(axis.title = element_text(size=10, face = "bold")) + 
    theme(panel.background = element_rect(fill = "grey95"))  +
    ggplot2::annotate(geom = "text", label = "Source:ABC Monitors", x = Inf, y = -Inf, color = "blue",size = 3,fontface = "italic",hjust = 1, vjust = -30)
</code></pre>

<p>Is it possible to dynamically set the position of the annotation?</p>