Piwik Version

 Piwik version: 3.0.4
 MySQL version: 5.5.5
 PHP version: 7.0.7 
 Browser: Mozilla/5.0 (X11; Linux x86_64; rv:55.0) Gecko/20100101 Firefox/55.0

Reproduce steps:
1) Go to a website statistics
2) Go to Visitor Map
3) Select a Country and then select the cities view
4) Maximize the Map
5) The overly visits points are still small in contrast to the map. (See the screenshot)

Normal

Maximize