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How Browse USGS By Category and Location Works

The USGS Thesaurus defines a high-level, tree-like hierarchy of categories that describe the science and products of USGS. This feature lets you move around the "tree" of the Thesaurus to explore the categories -- their definitions, how they're used, broader or narrower terms, etc. -- and find selected USGS web pages that contain more infomation about a category. Since most USGS information is spatial, the browse also lets you specify an area and selects USGS web pages that best fit that area.

Features of "Browse USGS" pages and what they mean.
Feature	What it means or does
Category	This "breadcrumb" traces a path back up the hierarchy of categories. Pick any "crumb" to see a broader term.
Location	Similar to Category, this "breadcrumb" shows the hierarchy of locations.
Narrower categories	This is a list of terms that are more specific than the selected category.
Related categories	These terms may be closely related to the chosen category, but are not shown in the Category "breadcrumb."
Change location	This set of pull-down menus lets you select another location. The choices you will be offered are sensitive to the current choice. For example, if the present location choice is Alabama, you will be offered a menu of counties in Alabama. The choices include: States Counties Hydrologic units (2-, 4-, 6-, and 8-digits) Nations Selected US regions Selected world regions
Definition	The is how USGS catalogers define terms to classify the URL's.
Used for	These are "non-preferred" terms that have meaning similar to the chosen category. For example, "acid deposition" is the preferred term for "acid rain." We include non-preferred terms in the Alphabetical Index of USGS Science Categories to help users who may be unfamiliar with the preferred terminology.
Search for Categories	If you're unsure about what category to choose, just type a phrase in the box. The software will try to match it to one of the USGS categories.
Alphabetical Index of Categories	This is a complete alphabetical listing of all USGS Thesaurus terms. Use this to help find a term.

Where to Start

You can start browsing right at the top of the "tree" to see the structure of the Thesaurus. Or, you may prefer to start with the Alphabetical Index of USGS Science Categories.

The Collection

The list of USGS Web pages with more information on categories comes from a collection of approximately 2,100 key USGS Web pages (out of more than 300,000 in over 300 USGS Web sites) selected by librarians, webmasters, and subject-matter experts to support the terms of the USGS Thesaurus. These pages are carefully cataloged by category and location.

"Browse USGS by Category and Location" is intended to help you find the most relevant links to the more general USGS topics. If you're looking for something very specific, you may find the USGS Search Engine (also accessed from the USGS home page) more effective.

Spatial Search

The spatial selection routine uses the bounding latitudes and longitudes of the area you select to find Web pages that best fit the selected area. Hence, if you select "Illinois," the selector will give the greatest preference to web pages about the State of Illinois, and lesser preference to web pages about Chicago (too small) or the United States (too big).

A big advantage of a spatial search based on latitude and longitude is that it doesn't depend on the complex relationships associated with names. Hence, a page about Chicago probably would be found when searching for "Cook County, Illinois" because their boundaries are similar.

The best-fit ranking method keeps national reports from dominating the search. As you might expect, USGS has a lot of pages about the United States. When looking for pages about Illinois, the best fit would be for reports specifically about Illinois. Since the bounds of Illinois are much smaller than the bounds of the United States, the national reports are ranked low. A report about the Illinois-Indiana region, however, would rank higher than one about the United States, but lower than one about Illinois. The procedure works the opposite way too: a search of "United States" would give lower rankings to local and regional reports.

To allow it to operate quickly, the spatial search is based on a bounding rectangle, not the detailed boundaries of the selected place. This works great for rectangular Colorado, and less well for, say, Massachusetts! The oddities that result tend to receive lower rankings. Nevertheless, it's not unusual to see some strange results down in the bottom of the list.