By Charlie Frye, Esri Chief Cartographer
Keeping track of scale ranges at which a layer will be visible when a map has a few scale ranges and dozens of other layers can quickly become mind-boggling. This entry describes a strategy for using ArcMap’s Table Of Contents (TOC) to create these maps and effectively manage all those layers and scales.
As you create a map that will cover several scale ranges, the recommended work flow is to create a group layer for each scale range. Another way to think of this is that a multi-scale map is just an ordered sequence of maps of different scales. At this point, I’ve found that in trying to verbally (or in writing) describe this to folks that a picture is extremely helpful; so I’ve included an example of the TOC of a hydrography map I made recently.
As I was making this map, I used group layers to organize layers by scale. Within each group layer my layers were essentially the same, i.e., there was a layer for Gages in my first five group layers. However, the symbols and labeling rules were revised for each scale.
I also used layer definition queries to select subsets of features for a given layer at each scale. The idea is to show fewer and larger or more important features at smaller scales. For example, in the Cities layer I used the land area of the city polygons as the basis for selecting which cities were shown at each scale. Thus, in the 1:75,000 group layer I showed all the cities; in the 1:150,000 group layer I showed the cities that were larger than 0.001 decimal degrees, and for smaller scales I used larger areas. For each group layer, I zoomed to the minimum and the maximum scale and checked several areas, and if necessary I refined my definition query so it included only the cities that made sense for those scales without being too sparse or too crowded and cluttered.
The main benefit of using group layers this way is that the group layer scale range is applied to all layers in the group layer. This makes it easy to adjust the scale ranges just once for all the layers in the group.
Another benefit is that once I had the symbology, labeling, and definition queries set for one layer at a given scale, I could copy it into another scale’s group layer by dragging and dropping that layer, and then just adjust the properties rather than define them from scratch.
TIP: Note how I’ve named my layers with short unique names. This makes using the Label Manager much easier.
Sometimes you will have the same kind of data, but from a more detailed data source. In this case, it may be possible to use the Import button on the symbology tab of the layer properties dialog. This will import the symbols you have set up on the smaller scale layer, making efficient work of that task.
Once you have the map working properly, i.e., only the features that are supposed to be displayed at each scale range are being displayed, you will likely need to publish the map. Unfortunately the easiest way to make the map is not the easiest way to use the map. The users of your map will want control visibility by simple, easy to understand layer names like Cities, Rivers, Boundaries, etc. To do that you can use group layers, but now the contents of each group layer will be a single theme of information and the layers will be set to use the appropriate scale range. Here is an example of how the map above was transformed:
In this case, the Basins layer is controlled by the viewer at the group layer level to turn it on or off, and this will work no matter what scale the map is currently shown.
The process of transforming the map is a bit repetitive as you will need to edit each layer. As a precaution, I first save my map with a different name. The nature of repetitive work being what it is; you, just like me, may get interrupted or side-tracked and it’s hard to come back to this task with a clear idea of where you were and what the next step should be.
The trick I use is to minimize such difficulty is to first go through each layer in a given map’s scale (from the table of contents above) and set all the layers to have the same scale range as their group layer does. It’s easier to do this at this point while you can still see the group layer’s scale range, which, believe me, is handy if you’re working late on a Friday. Then I turn off the scale ranges at the group layer level and pan and zoom around the map. Everything should still be working the same way. If everything is working well, save the MXD as a different name—that way you won’t lose any changes.
Next create new group layers, named after each theme of information (based on the layers in your map). Drag and drop layers from the old scale-based group layers to the appropriate new theme-based group layers.
TIP: Use Ctrl-Click and Drag: this will not copy the layers, but instead just move them between the group layers; that way you’ll know you’re done when the old group layers are empty. Delete the old group layers and save the MXD.
Last, test your work by panning and zooming around to make sure the newest map still functions like original.