March 6, 2017
By George Demmy
We recently got a question from a customer asking how to create GeoPDF maps that have features that turn on or off as you zoom in like the USGS US Topos do. Maps for America! I love it! But I digress. This behavior is something that most Web mapping or GIS types understand intuitively – when you’re zoomed out at a continental view, you don’t see Buford, Wyoming but you do see states and the like. However, when you zoom in, at some point, you see Buford and its Ames Brothers Pyramid. Some features in the US Topos have this scale-dependent property and it’s essential for the usability of those maps. Cartography is not the art and science of putting stuff at the geographically correct position relative to each other on a map – it’s making that geo-contextualized information useful. For the creation of PDF maps, this is where TerraGo Publisher really helps.
ArcMap lets map makers set a range of scales where a layer is visible. Different layers can have different ranges, and of course, the default is always visible regardless of the scale. Publisher lets you choose to propagate that behavior to the GeoPDF maps you create. But it lets you do more. Consider a hierarchy of related features, some you want visible in one range, others you want in another. They’re all the same thing – maybe it’s cities, districts, and neighborhoods, blocks, whatever – but you want different levels of detail depending on the view. Now imagine that pattern repeated a bunch of different times for a bunch of different feature classes. The ArcMap Table of Contents (TOC) is getting messier and messier to the point of becoming useless as a user interface in any generically-exported PDF. Moreover, much, or even most of the information in a map doesn’t need to be on a “layer” at all. With export, you get what you get.
However, with Publisher, you can present a clear, concise TOC in the layer pane with those elements which don’t need to be placed on separate layers pushed down onto the basemap and group related layers into a single logical layer. You can choose to have the logical layer be a indivisible item, or it can be opened to let its components be individually toggled on and off. You can name any item anything you want, regardless of how it appears in ArcMap, change the initial visibility state, whatever you want, all without having to alter your set up in ArcMap. And the scale-dependent visibility behavior remains determined by how the layer was configured in ArcMap regardless where it is represented in the GeoPDF layer configuration.
Preserving scale-dependent visibility and providing a means to present a simpler, clearer, and concise arrangement of layers in the resulting GeoPDF map (without affecting any of the set-up in ArcMap) are two of the most popular features of TerraGo Publisher and provide a clear illustration between the technology and attitude of publishing on the one hand and export on the other.