title: How would I change the shape of ggplot legend symbols?
body: <p>I am using ggplot to visualize the gapminder data set. Can someone help me get the legend to show round points with their sizes respective to the population of the country?</p>
  <pre class="lang-r prettyprint-override"><code>df1&lt;-gapminder[!(gapminder$country==&quot;Kuwait&quot;),]
  
  blackline &lt;- df1 %&gt;% 
    group_by(continent, year) %&gt;% 
    summarise(average = weighted.mean(gdpPercap))
  
  p &lt;- ggplot(data = df1, mapping = aes(x = year, y = gdpPercap)) + 
    scale_x_continuous(breaks = seq(1960, 2000, by = 20)) +
    theme_bw() +
    labs(x = &quot;Life Expectancy&quot;,
         y = &quot;GDP Per Capita&quot;,
          color = &quot;Continent&quot;,
          size = &quot;Population (100K)&quot;) +
    # colored dots
    geom_point(df1, mapping = aes(col = continent, size = pop/100000)) +
    # colored lines
    geom_line(data = df1, aes(color = continent, group = country)) +
    facet_grid(cols = vars(continent)) +
    # weighted average black line
    geom_line(data = blackline, aes(x = year, y = average, size = 1)) +
    geom_point(data = blackline, aes(x = year, y = average, size = 1000))
  
  p 
  </code></pre>
  <p><img src="https://i.stack.imgur.com/AtZlr.png" alt="ggplot output" /></p>