Pippa

gem 'pippa'
gem 'lulu'  # If you'd like to use the marker merge function

$ bundle install

$ gem install pippa
$ gem install lulu  # Again optional if you wish to merge

require 'pippa'

# Get available map names.
puts Pippa.map_names

# Make a new, clean map.
map = Pippa::Map.new('USA') # or 29 other maps (default == 'World')

# Change default dark red fill to dark green.
# Changes cause dots entered so far to be rendered to graphic.
# Several other parameters also control dot appearance.
map.fill = 'DarkGreen'

# Change default to enable ImageMagick anti-aliasing by refraining
# from snapping dot coordinates to nearest pixel.
map.anti_alias = true

# Remove overlaps of markers by repeated merging of the pair with
# greatest overlap, creating a new marker with area the sum of the
# merged ones. Merging occurs just before the accumulated markers
# are rendered. Uses a fast algorithm so that 10,000s of markers
# can be handled in a fraction of a second. Default is no merge.
# Requires the **lulu** gem, which is not an automatic dependency.
map.merge = true

# Add a dot in the middle of the map using pixel coordinates.
map.add_dot(map.width/2, map.height/2, 100)

# Add a single green pixel dot at West Point, NY.
# Between calls to render, dots are drawn biggest first, so
# overlaps are generally okay.
map.add_at_lat_lon(41.5, -74.1)

# Flush buffered dots to the map.
map.render

# Add a dot with an area of 86 at a given zip code in Pennsylvania.
# This will be drawn on top of all previous dots regardless of
# size due to render above.
map.add_at_zip('18088', 86)

# Make a blob of the map e.g. suitable for Rails send_data.
# Any RMagick blob format will work in lieu of 'png'
blob = map.to_png

# Write the map directly to a file using RMagick write.
# Any RMagick writable format will work.
map.write_jpg('mymap.jpg')