The reference scale for the map. The reference scale is the scale at which feature symbols and text will appear at their authored size. If the viewing scale is different from the reference scale, then the symbology and text graphics will be scaled to keep the same size on the map. Only those layers for which scaleSymbols is true will be scaled. For example, FeatureLayer.scaleSymbols.
The default value is 0.0. Zero reference scale means that no reference scale is set and all symbology and text graphics will be drawn at their default screen size.
Updates to the reference scale will redraw other layers that use the reference scale, and may redraw other layers that depend on them. For example, dynamic labels may need to re-position to avoid overlaps.