The World Hydro Basemap is THE reference basemap for natural resource professionals. This map shows relative flow of the rivers of the world at scales 1:147 million to 1:2.3 million globally, and in the United States we've used the National Hydrography Dataset, created by EPA and USGS, to create a small scale hydro basemap for the US down to 1:18 thousand. In this map, stream symbols of the same size and color represent roughly the same annual flow volume.
Using this technique to visualize our Earth's surface water produces an interesting view that has never been seen before in a multi-scale map.
The World Hydro Basemap also serves as the foundation that provides context for observational data, including water quality and quantity measurements, information about aquatic habitats such as fish and vegetation surveys, and water management and planning, just to name a few.
The World Terrain Base provides the elevation context necessary to understand why the world's surface water flows where it does.
The World Hydro Reference Overlay uses the same design as the original US Hydro basemap, and provides the streams, waterbodies, drainage areas, and cultural reference information necessary to make the World Hydro Basemap useful for scientists, professionals and researchers in the fields of Hydrology, Geography, Climate, Soils, and other natural sciences related to water. The World Hydro Reference Overlay is a cached PNG32 web map service with transparency, so that layers can be displayed under the overlay - following the 'Map Sandwich' design. The World Hydro Basemap contains the outer "bread" layers to which thematic water-related map services can easily be sandwiched in between, resulting in a beautiful and legible hydro map mash-up.
Use the World Hydro Basemap in your web maps and applications or in ArcGIS for Desktop as your hydrologic reference basemap.