Line symbols are used to draw linear features and graphics in maps, scenes and layouts.
Line symbols, like all symbol types, are composed of symbol layers. Line symbols typically contain one or more stroke symbol layers. Line symbols can also include marker symbol layers, to draw markers along their length or at the endpoints. Marker placement properties are included with marker symbol layers that are in line symbols. Rarely, line symbols also include fill symbol layers. In this case, Enclosing polygon symbol effect is also applied to dynamically create polygon geometry for the fill to draw. You can change the properties of the symbol effect or delete it and replace them with a different effect as long as you maintain geometric logic within the symbol.
Line symbol properties
The properties of line symbols come mainly from the properties of the symbol layers within them, but there are also some global properties you can adjust for the line symbol as a whole. These are called the basic properties of the symbol. You use the Properties tab in Format Symbol mode of the Symbology pane to access all of the properties of a line symbol. The symbol properties are contained across three tabs, as outlined in the following table.
Symbol tab | Access all the basic properties that apply globally to the line symbol. These are the only properties available when you have more than one line symbol selected. |
Layers tab | Access all of the properties of each symbol layer that makes up the line symbol. This is where you control the most detailed properties of the symbol's appearance and behavior. |
Structure tab | Access the way the line symbol is structured. On this tab you can add, duplicate, delete, and reorder symbol layers and symbol effects. |
Line symbol basic properties
Line symbols have two basic properties: Color and Line width. They apply globally to the whole line symbol. You'll find these on the Symbol tab 
. Basic properties are an easy way to make simple changes to a symbol. To make detailed changes to the symbol, you must access the properties of the individual symbol layers that make up the symbol on the Layers tab 
.
When you vary symbology—either the transparency, color, or size—of a feature layer by an attribute in the source data, it is the basic properties of each line symbol that are dynamically modified.
When you have more than one symbol selected, for example, when you are formatting all of the symbols in a layer symbolized by unique values, you can access only the basic properties of the symbols. You cannot see or change the properties of the individual symbol layers that make up all the selected symbols.
Color basic property
The Color basic property applies to all color-unlocked symbol layers within the line symbol.
When you vary the color of all symbols in a feature layer by attribute, only the color-unlocked symbol layers are affected. When you vary the transparency of all symbols in a feature layer by an attribute, the entire symbol is affected, regardless of how color locking is established within the symbol.
Line width basic property
The Line width basic property shows the width of the largest stroke symbol layer or the Size of the largest marker symbol layer in the symbol. If you change the Line width basic property, the widths all of the stroke symbol layers and sizes of all the marker symbol layers are resized proportionally. Values in effects and marker placements are also scaled proportionally. For example, if you double the width of a dashed line (a line that includes a stroke symbol layer with a Dash symbol effect applied), the Dash template values are doubled as well.
Scale-based sizing
When a line symbol symbolizes a feature layer in a multiscale map (as opposed to being a stand-alone symbol in a style, or a symbol applied to a graphic in a layout), you can check Enable scale-based sizing to adjust the line width of the symbol at different scales. Making line symbols narrower at smaller scales is an effective and easy way to reduce visual clutter and interference in a map. You cannot vary the size of line symbols by scale in a scene.
When enabled, a slider appears below the Line width property, with stops derived from the map scales. The slider itself extends across the complete scale range of the map, 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. The dark part of the slider shows the visible scale range of the symbol class. If this visible scale range has not been specifically set, the dark portion of the slider corresponds to the scale range of the feature layer. Click a scale stop and define the line width at that scale in the Line width property. You can drag stops to define the width at a different scale. You can click along the slider to add new stops based on the defined map scales. The line symbol width varies linearly between widths set at each scale. You should use scale-based sizing without a reference scale set.