The municipality of Benito Soliven is situated nearly at the center of the Province of Isabela.  It is bounded on the north by the municipality of Ilagan, the capital town of the province; on the east by the town of San Mariano; on the west by the municipalities of Naguilian and Cauayan City 

The municipality of Gamu, the oldest town in Mallig Plains, is located in the central part of the Province of Isabela.  It is approximately 10 kilometers away from the Provincial Capitol of Isabela and about 395 kilometers from the National Capital City of the Philippines, Manila.

It is bounded on the north by the municipality of Ilagan, or the northwest by the municipality of Quirino, on the south by the municipality of Reina Mercedes and on the southwest by the municipality of Burgos, and on the Southeast by the municipality of Naguilian.

Gamu has a total land area of 129.40 square kilometers with 16 barangays, 3 of which are classified as urban barangays, District I, II and III, and the rests are considered rural barangays.

Naguilian, one of the thirty four (34) municipalities and three (3) cities in the Province of Isabela, is located in Central Isabela.  It is bounded in the north by the municipality of Gamu; on the east by the municipality of Benito Soliven; on the south by the city of Cauayan; and on the west by the municipality of Reina Mercedes.

Naguilian is located approximately between 16 degrees, 55 minutes and 17 degrees east latitude and 121 degrees, 50 minutes and 121 degrees, 55 minutes north longitude.

Being centrally located, Naguilian is accessible from its neighboring municipalities.  From Gamu and Reina Mercedes, 6.14 kilometers and 5 kilometers, respectively, on the concrete-paved Maharlika Highway; or to Cauayan City, 15.04 kilometers southward along the paved Maharlika Highway.  Naguilian is also 20 kilometers from Ilagan, the Capital town of the province and 383 kilometers from Metro Manila.

Marked by highly differential physio-geomorphological formations, Palanan, especially the Poblacion is located inside a Valley-like fertile alluvial plain.  The Poblacion fronts  river delta draining fresh water to Palanan Bay along the Pacific Ocean.  Since Palanan is in the Pacific Belt of Fire, its land formation was attributed to volcanic activities or land movements due to tectonic phenomena.  The rich volcanic soil characteristics in the Municipality proves that land formation in the place was highly traceable from volcanic origin.

Palanan being part of the tropical zone, is exposed to relatively hot and humid environment.  Northeast monsoon and southeast monsoon creates remarkable wet and dry seasons.  These monsoons bring typhoon annually to Palanan destroying most of its crops as well as human properties. 

The adverse climatic conditions during the rainy season, the lack of industries and employment opportunities, the absence of an affordable transportation system as well as internal transport system and the absence of basic socio-economic facilities hindered the economic growth and physical development of Palanan.  In spite of this, however, human settlements continue as a result of the increasing population.

The town Palanan is located along Pacific Coast and situated on 122o9’ to 122o32’ East longitude and 16o 50” to 17o 10’ North latitude.  It is one of the coastal towns of Isabela. 

The Municipality of Reina Mercedes is situated in Central Isabela.  It is a satellite municipality of Cauayan, a growth center of the province of Isabela.  Its terrain is generally flat rolling.  It is bounded on the north by Naguilian; on the east by Cagayan River; on the south by Cauayan; and on the west by Luna.  The poblacion is approximately 23 kilometers south of Ilagan on the national highway and 10 kilometers north of Cauayan.

San Mariano has a total land area of 146,950 hectares. It constitutes 13.78 percent of the total land area of the Province and is considered as the largest town in the country.

The municipality lies in the eastern part of the Province of Isabela. It is bounded on the North by the Municipality of Ilagan, on the East by the Municipality of Palanan, on the South by the Municipality of San Guillermo and on the West by the Municipality of Benito Soliven. It is approximately 404 kilometers from Metro Manila and 46 kilometers from Ilagan, the provincial capital.

San Mariano is located approximately on the grid coordinates of 160 57’41” to 170 00’08” north latitude and 1210 58’39” to 1220 01’20” east longitude.