Wild trout stream hunters need good, detailed maps.   We care about not only the big streams, but also the 1st and 2nd order tributaries and their names.  We find a reference to "Hogstock Run" somewhere in Pennsylvania.  Where is it?  We care about old logging roads and hiking trails, because these features (often invisible in aerial imagery, even of the most detailed kind) may mean the difference between a brutal bushwhack or an easy hike into a stream.

This kind of information, historically, has only been available on topographic maps.  Even today, services like Google Maps provide only limited geographic place names, and very little information about hiking trails or unpaved roads.

Historically, topographic maps were created and maintained as images of the printed maps.  Today, increasingly, topographic maps are the output of massive GIS databases maintained by the USGS.  The information they contain is available not only as printed maps, but also as pdf files available for free download, and as "layers" in "The National Map", a free online web-viewer that's incredibly useful.

The National Map is available here: http://viewer.nationalmap.gov/viewer/
Note: the viewer seems to work in a variety of browsers, but is optimized for Firefox.  On a Mac, the map is usable on Safari, but some capabilities are not available.

Open the link, to view a map of the continental US, nicely rendered on a shadowed relief base layer.

The "good stuff" is hidden away.  Your first actions should be to open the "GIS Toolbox" and the "Overlays" windows.

Now you'll see a set of controls along the top, and data "overlays" on the left:

The "standard" controls in the GIS Toolbox allow you to pan the map  ("Hand"), or zoom in to areas of interest ("Magnifying Glass").  The "Base Data Layers" controls what information gets displayed on the map.  You can expand the listings by clicking on the "plus" signs in the layers box, and checking or unchecking layers to have them rendered (or not).

A very powerful feature of the National Map is that most geographic features, even tiny wild trout streams, are indexed and searchable. Here we've entered "Hogstock Run, PA" into the search box, and the system has located its mouth (Marker A).  You don't even need the state (though the search will take a lot longer).  Once we have a map with a marker, we can zoom in to see the area in great detail.

We can also view a "topo" map of the area by clicking on the "Content" tab at the bottom of the Overlays Box, and checking the box next to "Scanned Topo Maps".  This shows detail such as hiking trails (there is a trail, shown as a dotted line along the stream, though it's hard to see in the reduced resolution of the gif image shown below).  Confusingly, there's another layer called "US Topo Maps" in the data layers window.  It displays the names of the USGS topo map "Quads", and allows you to order PDFs of any given map online (free), or to order printed maps (for a fee) via the USGS online "Map Store".

However, for most purposes you don't need to bother ordering a complete "quad".  A very nice feature of the National Viewer is that it will render a custom PDF of the map you see on the screen.  This is typically easier to print and take with you on the stream than a full quad.  To do this, just click on the print link at the top of the viewer (NOT the print menu of your browser) and follow the prompts.  The USGS server will then generate the PDF within a few seconds, and provide a link for you to download it.

This little demo barely touches the surface of what's possible with the National Map.  Among the data layers accessible here is the complete National Hydrographic Database (NHD) which catalogs virtually every stream in the US.  Virtually every standard "place name" is indexed and searchable.  In the original version of this site, created in 2006, we recommended a couple of commercial vendors of web based  topo map services.  No more.  The National Viewer, along with the USGS' "Map Store" is now providing free services that are better than used to be available for a fee.