Optimizing map symbols for performance
By following certain design considerations, you can create symbols that maintain a better level of display performance. The type and complexity of each symbol you choose has a direct effect on map drawing performance, in addition to exporting, printing, and serving maps.
Below are some guidelines for maintaining performance when creating symbols for your map.
To maintain good drawing performance with marker symbols, you should
- Use simple style markers when you can. Marker symbols composed of multiple layers draw slowly because each additional layer effectively multiplies drawing time.
- Use a picture marker symbol in place of a halo. Halos are the single biggest contributor to poor marker drawing performance. Rather than using halo masks as a background behind a marker, create an .emf file that represents the symbol and a built-in halo background.
- Use simple shapes when possible. Marker symbols composed of extremely complicated shapes, such as those in the Conservation and other styles, increase drawing time.
- Set marker symbol properties to a size smaller than 60 points, since larger markers render slowly.
- Minimize the use of picture marker symbols, particularly if they are larger bitmaps or metafiles. When using picture marker symbols, the format of the source graphic file can impact performance. When the marker symbol has only one color, .emf files provide better performance than .bmp files. However, when a symbol has two or more colors, .bmp is the better-performing format.
Line symbols can be somewhat problematic when it comes to keeping their drawing performance at respectable levels while getting the detail or cartographic quality needed for your map. Of course, simple line symbols are the easiest answer when you want to reduce display times; however, these offer few options for diverse symbology other than thickness and color.
Cartographic lines, which are the most commonly used line symbol, can get relatively sluggish as more options are added. For example, adding a pattern template can result in more than double the drawing time as that of a solid cartographic line symbol. If you add an offset value or increase the width, the time to refresh the layer may double yet again. When it comes to line symbols, using fewer options will help reduce your display times.
One of the easiest ways to improve performance when drawing lines is to utilize line symbols from the ESRI_Optimized style, which contains symbols designed to perform better while appearing similar to their counterparts within the default ESRI style. The line symbols in the ESRI_Optimized style use fewer layers and reduced widths to improve performance. To learn more about working with line symbols in the optimized style, see Creating line symbols.
Here are some guidelines for maintaining good drawing performance with line symbols:
- Often you can achieve the identical appearance using a simple line instead of a cartographic line, especially for the outline of polygon symbols. Line symbols composed of multiple layers will increase drawing time.
- When using multilayer symbols, avoid mixing symbol types. It is better to use two cartographic line layers than to mix a cartographic and a hash layer into the same symbol. This is because the dataset rendering must be cycled through once for each layer type. For example, if you combine a cartographic and hash line symbol, as is done in a basic railroad-style line symbol, the data is drawn once for the cartographic symbol and again for the hash symbol.
- Use offset or dash patterns sparingly as they will increase drawing time. However, there are a few methods you can use to improve performance with these symbol types. For example, if the line width is less than one point, try using a simple line symbol rather than a cartographic line symbol. While the simple line symbol is optimized to draw faster, it may not handle drawing around acute angles as well. In addition, use only basic templates and minimize the unique mark and gap combinations and offset distances.
- Wide lines and lines with decorations, such as markers and arrows, draw more slowly. This is particularly so when symbolizing a large number of features.
One of the easiest ways to improve performance when drawing polygons is to utilize fill symbols from the ESRI_Optimized style, which contains symbols designed to perform better while appearing similar to their counterparts within the default ESRI style. The symbols in the ESRI_Optimized style use fewer layers and reduced widths to improve performance. The picture fill symbols use .emf files versus the bitmaps that are used in the default style. To learn more about working with fill symbols in the optimized style, see Creating fill symbols.
Here are some guidelines for maintaining good drawing performance with polygon symbols:
- When symbolizing polygons, simple fill symbols without outlines will draw the quickest.
- When you need an outline around the polygons, keep it simple, since complex outlines mean longer drawing times. You should choose a simple line symbol whenever possible. As long as the outlines require only a solid line as the boundary, the simple line symbol is your best choice. Otherwise, other line types, such as cartographic, marker, and hash, will considerably increase the drawing time. Use cartographic line symbols when you need to make use of the properties and enhanced print quality they provide, following the performance guidelines discussed in the previous section.
- Use a minimal number of layers to make up your fill. As with other symbol types, fills composed of multiple layers will slow down drawing because each additional layer effectively multiplies drawing time.
- Dot density fills, particularly with a masking layer, draw more slowly and should not be used unless the number of dots is low enough to allow acceptable drawing speeds.
- When working with line fills, use simple lines for both the fill and outline.
- For picture fills, when the symbol has only one color, .emf files provide better performance than .bmp format files. However, when a symbol has two or more colors, .bmp is the better-performing format.
Other symbology considerations
Other symbology techniques, including symbol level drawing and variable-depth masking, can greatly degrade drawing performance because of the additional processing required to display their effects. For example, symbol level drawing allows you to specify the order in which symbols and symbol layers for multilayer symbols are drawn on your map—overriding the default ArcMap drawing sequence. Masking is often used to clarify the legibility of a map that is densely packed with text and feature symbology.