title: Set marker size in plotly
body: <p>How can I change the marker size in plotly in R on a map? If I set the <code>size</code> argument to any number it makes it the same, too big size. And if I map it to a variable in my data, the markers are to small to really be able to tell the difference in the first place. Ideally I would like to increase the base size and keep the proportional aspect through mapping to the variable.</p>
  
  <p>Reproducible example:</p>
  
  <pre><code>library(data.table)
  library(plotly)
  library(dplyr)
  
  sample &lt;- data.table(Region=c("Illinois","Illinois","California","California","Texas","Texas"),
                       code=c("IL","IL","CA","CA","TX","TX"),
                       Group=c("A","B"),
                       Value=rnorm(6, mean=100, sd=6))
  
  sample[Region=="Illinois", c('lat', 'long') := list(40.3363, -89.0022)]
  sample[Region=="California", c('lat', 'long') := list(36.17, -119.7462)]
  sample[Region=="Texas", c('lat', 'long') := list(31.106, -97.6475)]
  
  
  x &lt;- list(
    scope = 'usa',
    projection = list(type = 'albers usa'),
    showlakes = F,
    lakecolor = toRGB('lightblue')
  )
  
  sample %&gt;%
    plot_geo(
      locationmode='USA-states'
    ) %&gt;%
    add_markers(
      y=~lat, x=~long, hoverinfo="text",
      color=~Group,
      text=~Group, size=~Value
    ) %&gt;%
    layout(
      title='plotly marker map',
      geo=x
    )
  </code></pre>