CartoDB + CartoCSS example used in Hacking Science demo January 11, 2013.

accidents2010.csv

Map Style.css

/* Visualize overall trends with point intensity
** using basic compositing options.
** Try changing 'lighten' to 'multiply' and see
** what happens.
************************************************/
#accidents2010::intensity {
    first/marker-fill: #642A73;
    first/marker-opacity: 0.01;
    first/marker-width: 80;
    first/marker-line-width: 0;
    first/marker-placement: point;
    first/marker-allow-overlap: true;
    first/marker-comp-op: lighten;
  
    second/marker-fill: #642A73;
    second/marker-opacity: 0.02;
    second/marker-width: 50;
    second/marker-line-width: 0;
    second/marker-placement: point;
    second/marker-allow-overlap: true;
    second/marker-comp-op: lighten;
  
    third/marker-fill: #FF7936;
    third/marker-opacity: 0.04;
    third/marker-width: 20;
    third/marker-line-width: 0;
    third/marker-placement: point;
    third/marker-allow-overlap: true;
    third/marker-comp-op: lighten;
  
    fourth/marker-fill: #FFEE00;
    fourth/marker-opacity: 0.04;
    fourth/marker-width: 10;
    fourth/marker-line-width: 0;
    fourth/marker-placement: point;
    fourth/marker-allow-overlap: true;
    fourth/marker-comp-op: lighten;
}

/* Make the map symbology responsive to map scale. 
** Switch to individual points at zoom level 9 or
** higher, and scale symbols by # of fatalities.
************************************************/
#accidents2010::point[zoom >= 9] {
    marker-fill: #D3B4DB;
    marker-opacity: 0.5;
    marker-width: 5 + (7 * [fatals]);
    marker-line-width: 2;
 	marker-line-color: #925CA1;
  	marker-line-opacity: 1.0;
    marker-placement: point;
    marker-allow-overlap: true;
}

/* If a drunk driver was involved, change the
** symbol color to cyan.
************************************************/
#accidents2010::drunk[zoom >= 9][drunkdriver=true] {
    marker-fill: #89FAED;
    marker-opacity: 0.5;
    marker-width: 5 + (7 * [fatals]);
    marker-line-width: 2;
 	marker-line-color: #288294;
  	marker-line-opacity: 1.0;
    marker-placement: point;
    marker-allow-overlap: true;
}