code: public synchronized void scaleStrokeWidth(float scaleFactor, byte zoomLevel) {
          if (!strokeScales.containsKey(zoomLevel) || scaleFactor != strokeScales.get(zoomLevel)) {
              for (int i = 0, n = this.rulesList.size(); i < n; ++i) {
                  Rule rule = this.rulesList.get(i);
                  if (rule.zoomMin <= zoomLevel && rule.zoomMax >= zoomLevel) {
                      rule.scaleStrokeWidth(scaleFactor * this.baseStrokeWidth, zoomLevel);
                  }
              }
              strokeScales.put(zoomLevel, scaleFactor);
          }
      }
docs: Scales the stroke width of this RenderTheme by the given factor for a given zoom level
  
  @param scaleFactor the factor by which the stroke width should be scaled.
  @param zoomLevel   the zoom level to which this is applied.