Multiscale maps are dynamic maps that display data in different ways across a range of scales. They differ from static maps, which are designed to be viewed and output at a single scale. You can zoom in and out on any map, but multiscale maps are authored specifically to ensure visual continuity at all scales so the map communicates effectively. Multiscale maps are most effective when they approach a near-seamless depiction of data over a wide variety of scales. To best achieve this, ensure that you symbolize data appropriately, yet similarly, across all scales. Ideally, your aim is subtle changes to feature density across scales to avoid distraction from the map's content and overall message.
There are two important considerations when authoring a map intended to be viewed at a variety of scales. The first is an awareness of the scale at which the data was captured or otherwise created. The geometry and position of geographic features are at a resolution and precision that is intrinsic to the scale of their sources. When the data is displayed on a map at exactly this scale, appropriate feature density and precision are maintained. Displaying data at a smaller scale than capture scale is acceptable, but display at a larger scale is not, because it implies a greater degree of precision and inclusion than what is present in the data.
Second, while data can be displayed validly at scales smaller than the creation scale, be aware that at smaller scales, too much data and detail can be cumbersome, and draw performance may be impacted. Individual features and feature details may be indiscernible at scales smaller than that for which the data was intended. An effective multiscale map is one that uses data thinning and other generalization methods to show an appropriate amount of data at each scale range. Not only do these methods make your map more readable, they make it smaller and draw faster.
There are three main approaches to intelligently and efficiently limiting what is shown in a map at each scale. First, you can use generalization to alter the feature geometry used in your map. Second, you can adjust the properties of the map layers to limit which features draw relative to the view scale. Finally, you can adjust how the layer symbology draws relative to the view scale. Typically, you employ a combination of all three when authoring multiscale maps.
Control the display at scale boundaries
When setting scale ranges—either on map layers or on symbols—it is important to understand what happens at the boundaries of those scale ranges. You want to avoid two versions of a feature drawing simultaneously at scale boundaries, but also avoid a small scale gap where neither version of the feature draws. There is a map property that manages this case. Set your scale ranges to start and stop at exactly the same scale value. Then, in the Contents pane, right-click a map and click Properties to open the Map Properties dialog box. On the General tab, ensure that the Draw up to and including the maximum scale in scale ranges check box is not checked. It is not checked by default on new maps. This is an especially important strategy if you intend to create vector tiles from the map. This setting applies anywhere in the map where scale ranges are specified.
To avoid showing features from both layers when viewing your map at scale range boundaries, it is common practice in ArcMap to set the Out Beyond scale range property of the more detailed layer to be one scale unit less than the In Beyond scale range property of the more generalized layer. The drawback with this approach is that you can create a situation in which no data at all draws at the interim scale. For this reason, maps created by importing .mxd files have Draw up to and including the maximum scale in scale ranges checked by default. Consider re-authoring scale range extremities to be equal on imported map documents and unchecking this box.
Before you concern yourself with what is visible at each scale range, determine whether your feature geometry is appropriately detailed for the scale ranges you want to display. Everything placed on a map must compete for page space and legibility, especially as the scale gets smaller. Some features that are not tangibly visible in the landscape—such as contour lines or administrative boundaries—must be drawn and labeled on a map alongside all the apparent features such as roads and waterways. Some features must be drawn with symbols larger than their corresponding ground size to be legible. These realities contribute to the overlap of graphics, which is exacerbated by reductions in scale. Generalization is the process of deciding which features to keep, which to eliminate, which to exaggerate, and which to simplify to retain appropriate and legible feature density at smaller scales. The challenge lies in how to depict geography as faithfully as possible while reducing extraneous detail and preserving clarity and intent. Generalization geoprocessing tools reduce feature detail and density to make data more appropriate for display at smaller scales.
Some generalization processes consider individual features in isolation. You can usually remove detail from building outlines, or smooth small bends in streams without impacting other features. However, some processes must account for the spatial and contextual relationships among the features, even those from different layers, whose collective patterns are a visual characteristic of the landscape. For example, a process that simplifies collections of individual building features into built-up area polygons should also consider the location of major roads, water features, administrative boundaries, and land-use zones.
You can significantly reduce the amount of data in a multiscale map by generalizing your data with the following tools:
- Aggregate Polygons
- Eliminate Polygon Part
- Merge Divided Roads
- Simplify Building
- Simplify Line
- Simplify Polygon
- Simplify Shared Edges
- Thin Road Network
If you are working with a lot of data that must be considered contextually with other layers, you can also use the Cartographic Partitions geoprocessing environment variable to process the data sequentially by partition to avoid exceeding memory limitations. See Generalizing large datasets using partitions for more information.
If you need to resolve symbol conflicts at a smaller scale, consider first processing your data in ArcMap using the tools in the Graphic Conflicts toolset in the Cartography toolbox. See Understanding conflict resolution and generalization for more information.
Adjust layer properties
In addition to generalizing feature geometry, there are some layer properties that you can set to limit what is drawn for each layer. You can specify a definition query to limit the layer to only a subset of the source data's features, limit the scale range for the layer, or write display filters to control which features are shown at different scales. These approaches can be used independently or in conjunction with one another.
Limit the features in a layer with a definition query
If your data is well attributed, one of the easiest ways to reduce the number of features displayed is to set a definition query on a layer. This limits the visible features by category or more complex query. An example of this is a query on polygon areas to display only buildings larger than a certain size.
To set up a definition query, complete the following steps:
- Right-click a layer in the Contents pane and click Properties.
- On the Layer Properties dialog box, click the Definition Query tab.
- Add one or more clauses to define a limited set of features to display in the layer.
Another example is to remove alleyways and footpaths from a layer of roads. Be aware, however, that if you want to show these feature categories at a larger scale, you'll need to duplicate the layer and use a different definition query. There are different approaches you can use that avoid the duplication of layers. See the sections below on display filters and refining the visible scale range of symbol classes for strategies to avoid the duplication of layers. These approaches are particularly important if you're making a map from which you'll create vector tiles. To learn more about creating vector tiles, see Author a map for vector tile creation.
Limit the scale range of a layer
Adjust the visible scale range of a layer or a group layer to ensure that those features appear only when the scale and surrounding feature detail can support them while maintaining visual clarity. This is an easy way to limit a whole layer to the appropriate scale range for its level of detail.
It's common to make many copies of a layer and set visible scale ranges differently on them in conjunction with different definition queries. This is a valid technique, but it requires duplicating layers that can be difficult to manage, store, and manipulate in the Contents pane. (This amounts to duplicated information if vector tiles are created from the map.) It may be better to manage the visible scale ranges of categories of data in a layer by symbolizing it by unique values or graduated colors and adjusting the scale range of each symbol class.
To limit the scale range of a layer or group layer, complete the following steps:
- Click a layer or a group layer in the Contents pane.
- On the Feature Layer tab, in the Visibility Range group, define limits to the visible scale range by choosing scale values for either or both the In Beyond and Out Beyond values.
You can also define the limits of the visible scale range on the General tab of the Layer Properties dialog box.
To learn more about setting the visible scale range of a layer, see Display layers at certain scales.
Limit visible features at scale ranges with display filters
Display filters are like definition queries applied at scale ranges. They specify the features to draw at each scale within the confines of the scale range of the whole layer. Unlike the definition query of the layer, display filters only limit the drawing of features on the map or scene. The features that don't participate in the query are still available in the layer. You can identify, select, and edit them. They appear in the layer's attribute table and participate in analysis operations.
See Use display filters for more information.
Limit the labels that appear at each scale range
In addition to limiting the visible scale range of a layer, you can also manage the visible scales of label classes in a layer. Reducing excessive labels at inappropriate scales can dramatically improve both the clarity and draw performance of your map.
- On the Feature Layer tab set, on the Labeling tab, in the Visibility Range group, define limits to the visible scale range by choosing scale values for either or both the In Beyond and Out Beyond value.
To learn more about label class properties, see Use label classes.
Adjust symbology properties
Once a layer has been symbolized, there are additional steps that you can take to further control the amount of detail shown at each scale. You can adjust the size of symbols throughout the scale range of the layer to ensure they are sized appropriately in relation to other features at larger scales, but not visually overwhelming at smaller scales. With symbol classes established, you can adjust the visible scale range for each class, and even apply different symbols throughout that range. Understand that these settings relate to the symbology of the layer. If you change how the layer is symbolized, these settings are lost.
Refine the size of features by scale
To reduce visual density at smaller scales, another strategy is to reduce the size of symbols at smaller scales in the visible range.
The idea is to make subtle adjustments to symbol size such that the size is appropriate for the feature density at each scale, without introducing distracting, obvious size changes. An example is adjusting the size of the symbol used to draw streets. At large scales, you want streets to be appropriately wide as they run between buildings. If they are too narrow, they'll look unnatural relative to the buildings or other nearby features and won't adequately represent the landscape. At much smaller scales, you may still want to draw these streets to get an indication of urban density, but you want them to be thin enough to not interfere with other more important features and not be visually overwhelming.
See Scale-based symbol sizing for more information. Scale-based symbol sizing is only available in 2D maps. It is not available in 3D scenes.
Refine the visible scale ranges for symbol classes
In addition to specifying the visible scale range of an entire layer and setting up display filters, you can further refine the scales at which individual symbol classes are visible when the layer is symbolized with unique values or graduated colors symbology. This can limit the amount of detailed data that draws at smaller scales without having to separate or duplicate data in multiple layers. For example, you may have a roads layer in which you want to show major thoroughfares at all scales, but minor roads only between mid-scale and large-scale ranges, and footpaths only at the very largest scales. The Contents pane dynamically updates as you zoom in and out, showing only those symbol classes that are in view for the current view scale.
See Scale-based symbol classes for more information.
Show different symbols at different scales
In addition to defining which symbol classes appear at which scale ranges, you may want to refine the multiscale display further by assigning different symbols to different subparts of the visible scale range. Especially if you are using complex symbols at large scales, an effective way to reduce visual clutter at smaller scales is to switch to a simpler symbol that is still visually related. For example, symbolize minor roads as light orange with a thin, gray casing at larger scales, but just as a single, solid gray line at smaller scales. In this example, these lines would be defined as two separate symbols for the same symbol class. The gray color ties the symbols together so it is clear they are referencing the same features, but the uncased solid lines at smaller scales are visually simpler and take up less map space.
See Use scale-based symbol classes for more information.
There are numerous strategies you can employ to craft a compelling map that spans across a wide scale range. Use these strategies in conjunction with one another to effectively balance the amount of data, the level of detail, and the continuity of the map's message.