Vary the size of symbols by scale

Scale-based symbol sizing is a technique used to ensure that features retain appropriate relative sizes as map scales change.

The size of symbols can be adjusted dynamically across their visible scale range to reduce visual density at smaller scales while retaining an appropriate relative size at larger scales. Typically, these differences in symbol size are subtle across the visible scale range. You want to maintain a symbol size appropriate for the feature density at each scale without introducing noticeable increases in size.

A common example is adjusting the size (width) of the line symbol used to draw streets. The first, smaller image below shows the width of a line symbol for streets sized appropriately relative to the buildings at small scales (zoomed out). The larger images that follow show the same data at a larger scale (zoomed in). If the width of the line symbol does not change with the scale change, as in the image on the left, the streets look unnaturally narrow relative to the buildings and other nearby features. At smaller scales, streets should be narrow enough to not interfere with other more important features, yet still give an indication of urban density. The larger image on the right shows the same data and symbols at the same scale, but now the width of the streets is dynamically sized to draw larger at larger (zoomed in) scales.

At a relatively small scale (1:12,000), the width of the streets is appropriately sized in relation to the buildings.

At a larger scale (1:4,000), the width of the streets is too narrow in relation to the buildings (left), unless variable sizing is applied (right).

Scale-based symbol sizing is a property of a symbol, when it is used in the context of a feature layer in a 2D map. It is not available in 3D scenes. Because scale properties may differ between layers, scale-based symbol settings are not preserved when the symbol is saved to a style.

In addition to varying symbol size by scale, you can also vary it by attribute. See Vary symbology by size to learn how.

Understand the scale-based slider control

You set up scale-based sizing using a scale-based slider control in the Format Symbol mode of the Symbology pane

The slider represents the complete scale range, from an infinitely small scale (zoomed far out) on the left extreme of the slider, to a large scale of zero (zoomed very far in) at the right extreme of the slider. The thick, dark part of the slider shows the visible scale range of the symbol class. This is based on both the scale range of the symbol class and the scale range of the whole layer. Thinner parts of the slider show scales outside the visible scale range. If the visible scale range is not constrained to specific scales for the corresponding feature class, the entire slider is a thick dark line.

Along the length of the scale slider, small vertical rectangles indicate scale stops, specific scales within the scale range. Hover over a stop to see its scale value. These scale values are determined by the scales specified for the map. See Map scales and scale properties to customize the list of map scales.

A different symbol size can be set for each scale stop, to vary the size of the symbol along the scale range. The size between stops is calculated linearly between the values. A minimum of two scale stops are shown, but you can add more. Click-drag a stop along the slider to change its scale, which is identified on the tooltip.

To set the size value for a stop, click the stop rectangle. A selected stop is solid; unselected stops are hollow. With a stop selected, set the size of the symbol at that scale. Repeat for additional scales.

For a simple linear progression of sizes across the visible scale range, you can define the symbol sizes at only the smallest and largest scales, respectively. The size is interpreted smoothly and linearly between adjacent stops. For a nonlinear progression across the visible scale range, add more interim stops along the slider to customize the symbol size at those scales.

Apply scale-based sizing to a symbol

To use scale-based sizing, complete the following steps:

1. Highlight a feature layer by clicking its title in the Contents pane.
2. On the Feature Layer tab, in the Drawing group, click Symbology to open the Symbology pane.
3. Click a symbol to open the Format Symbol pane.

   Alternatively, you can click a symbol in the Contents pane to open the Format Symbol pane directly.

4. On the Properties tab, on the Symbol tab , check Enable scale-based sizing.

   A slider appears, representing the complete scale range, from an infinitely small scale (zoomed far out) on the left extreme of the slider, to a large scale of zero (zoomed far in) at the right extreme of the slider. Rectangles indicate scale stops at specific map scale values.

5. Hover over a scale stop to see its scale value. Click a scale stop to select it.
   1. Optionally, click-drag along the slider to set it at a different scale value.
   2. To add more scale stops, click an empty part of the slider, or click the Add size stop button .

   The selected scale stop is a solid rectangle. Unselected scale stops are hollow rectangles. The point symbol size varies linearly in size between stops.

6. With a scale stop selected, set the Size (point symbols) or Line width (line symbols) or Outline width (polygon symbols). Generally, larger symbol sizes are used at larger (more zoomed in) scales. Repeat this for the other scale stops.
As the map draws at different scales, the size of the symbol varies along the scale range.