docs: function(name, url, extent, size, options) {
          this.url = url;
          this.extent = extent;
          this.maxExtent = extent;
          this.size = size;
          OpenLayers.Layer.prototype.initialize.apply(this, [name, options]);
  
          this.aspectRatio = (this.extent.getHeight() / this.size.h) /
                             (this.extent.getWidth() / this.size.w);
      }