US EPA Level III and Level IV Ecoregions
收藏资源简介：
<font size='2' style='color: rgb(77, 77, 77); font-family: '><span style='color: rgb(77, 77, 77); line-height: 21px; background-color: rgb(255, 255, 255);'><font color='#000000'>This Map Image depicts the Level III and Level IV Ecoregions throughout the United States. The purpose of this map is to show Ecoregions that denote areas of general similarity in ecosystems and in the type, quality, and quantity of environmental resources. The intended audience is for the general public. There are two grouped layers in this map, Level III Ecoregions and Level IV Ecoregions. <br /><br />The first layer represents Level III </font></span></font><a href='http://www.georgewright.org/121omernik.pdf' style='color: rgb(33, 117, 155); text-decoration: underline; outline: none !important; font-weight: normal; font-family: ' target='_blank'>Omernik </a><font size='2' style='color: rgb(77, 77, 77); font-family: '><span style='color: rgb(77, 77, 77); line-height: 21px; background-color: rgb(255, 255, 255);'><font color='#000000'>Ecoregions. At Level III, the continental United States contains 104 regions whereas the conterminous United States has 84 (US Environmental Protection Agency, 2005). Level IV ecoregions are further subdivisions of Level III ecoregions. </font></span><span style='color: rgb(77, 77, 77); line-height: 18.4px; background-color: rgb(255, 255, 255);'><font color='#000000'>The second grouped layer represents Level IV Omernik Ecoregions. Level IV ecoregions are intended for large geographic extents (i.e. states, multiple counties, or river basins). Compilation of the level IV maps have been performed at 1:250,000 scale. For more information about Omernik ecoregions or to download ecoregion maps and GIS data, go to:</font><a href='http://www.epa.gov/wed/pages/ecoregions.htm' style='color: rgb(33, 117, 155); text-decoration: underline; outline: none !important; font-weight: normal;' target='_self'><font color='#0000ff'>http://www.epa.gov/wed/pages/ecoregions.htm</font></a><font color='#000000'>. For additional information about this mapping service or to obtain the ecoregion data used to create the service, contact US EPA GIS Agency Central Support, </font><a href='mailto:esrisupport@epa.gov' style='color: rgb(33, 117, 155); text-decoration: underline; outline: none !important; font-weight: normal;'><font color='#0000ff'>esrisupport@epa.gov</font></a><font color='#000000'>.</font></span></font>
