In our Louisiana bird book draft, we use the terms below with respect to Louisiana geography. These are arbitrary boundaries that are in many ways unsatisfactory, as in any attempt to inflict typological categories on a continuum.
o Northern Interior = north of 31o
30' (but also south of that latitude to include southern extremes
of Sabine, Natchitoches, Grant, LaSalle,
Catahoula, and Concordia). This line corresponds
roughly to the boundary between USDA Plant Hardiness Zones 8a
and 8b. When divided into "western" and "eastern"
sections, the boundary is arbitrarily placed at the eastern boundaries
of Union (e.g., Ouachita R.), Jackson, Winn,
and Grant parishes, and thus the western boundaries of
Morehouse, Ouachita, Caldwell, and LaSalle
o Southern Interior = between the Northern Interior and Coastal Zone. When divided into "western" and "eastern" sections, the boundary is arbitrarily placed at the eastern boundaries of Rapides, Evangeline, St. Landry, and St. Martin parishes, and thus the western boundaries of Avoyelles, Pte. Coupee, Iberville, and Assumption parishes; thus the Atchafalaya River roughly corresponds to the boundary.
o Coastal Zone = from the coastline and southern shore of Lake Pontchartrain to about 25 miles inland; also coastal islands, including the Chandeleur chain. [Thus, examples of towns considered within the Coastal zone are Hackberry, Abbeville, New Iberia, Franklin, Morgan City, New Orleans, LaPlace, Reserve, and Slidell; and towns just north of the Coastal Zone are Holmwood, Lake Arthur, Gueydan, Kaplan, St. Martinville, Thibodaux, Donaldsonville, and Mandeville. For convenience, we use the political boundaries of the following coastal tier parishes to delimit the Coastal Zone even if they include some area beyond the 25 mile limit: Cameron, Iberia, St. Mary, Terrebonne, Lafourche, Jefferson, Plaquemines, St. Bernard, Orleans, St. Charles, St. John the Baptist, and St. James. This leaves Vermilion and St. Tammany as the only two parishes split between Coastal and Southern Interior. When divided into "western" and "eastern" sections, the boundary is arbitrarily placed at the Iberia/St. Mary boundary.
o Offshore = Gulf of Mexico, more than 1 mile from the beach.
Nothern Interior (western) = (Caddo, Bossier, Claiborne,
Lincoln, Union, Webster, Jackson,
De Soto, Red River, Bienville, Natchitoches,
Sabine, Winn, and Grant).
Nothern Interior (eastern) = (Morehouse, W. Carroll, E. Carroll, Ouachita, Richland, Madison, Caldwell, Franklin, Tensas, LaSalle, Catahoula, and Concordia).
Southern Interior (western) = (Vernon, Rapides, Beauregard, Allen, Evangeline, St. Landry, Calcasieu, Jefferson Davis, Acadia, Lafayette, St. Martin, and n. Vermilion).
Southern Interior (eastern) = (Avoyelles, Pointe Coupee, W. Feliciana, E. Feliciana, Iberville, W. Baton Rouge, E. Baton Rouge, St. Helena, Tangipahoa, Washington, Livingston, Ascension, Assumption, and most of St. Tammany).
Coastal Zone (western) = (Cameron, s. Vermilion, and Iberia).
Coastal Zone (eastern) = (St. Mary, Terrebonne, Lafourche, Jefferson, Plaquemines, St. Bernard, St. James, St. John, St. Charles, Orleans, and extreme se. St. Tammany).