R: color gps points that show up more times darker in color
<p>I would like to plot gps points like a heat map - those that show up more times will be darker/warmer in color.
My data look like this:</p>

<pre><code>       lon   lat Freq
1  -121.93 68.28    1
2  -117.72 70.72    1
3  -110.69 68.75    1
4   -94.79 61.03    1
5   -93.80 58.63    1
6   -92.18 62.88    1
7   -89.68 46.15    3
8   -83.00 62.50    1
9   -78.99 56.41    1
10  -78.87 56.39    1
11  -71.30 65.95    1
12  -67.36 62.84    1
13  -67.35 62.86    1
14  -67.25 63.45    2
</code></pre>

<p>I can plot these data as follows:</p>

<pre><code>newmap&lt;-getMap(resolution="low")
plot(newmap)
points(data3$V5, data3$V4, col = "red", pch = 15, cex = 0.5)
</code></pre>

<p><a href="https://i.stack.imgur.com/pWMDr.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/pWMDr.png" alt="enter image description here"></a></p>

<p>However, I would like the points that have a frequency of 2 or 3 (see Freq column) to be darker/warmer like a heat map, with an accompanying legend. It looks like there might be a solution using ggmap, but I have not been able to obtain a world map using ggmap. (I need a world map because I will be plotting far more gps points than in this example that cross the globe). I like the way this outline of the world looks.</p>