Location, size and limits. Guipúzcoa is located on the edge of the Cantabrian Sea, at the bottom of the Bay of Biscay, bordering Laburdi and 42° 58' 10" and 43° 8' 5" north latitude and 1° 5' 13" and 1° 56' 47" east longitude in relation to the Madrid meridian. The surface area of the territory of Gipuzkoa is 1,996 kmz. From Txapitelako-arria, in Endarlaza, the border Gipuzkoa and Laburdino is marked by the course of the Bidasoa to its mouth in the bay of Txingudi. On the right bank are Biriatu (Laburdi), Behobia (L) and Endaia (L). On the left bank are Behobia, Irún and Fuenterrabía (Gipuzkoa). In the shelter of Cape Higuer is the port of Asturiaga. From this point, the coast begins to slope southwards as far as the Orio estuary and Zarauz beach. In this stretch Higuer and Zarauz, the coastline skirts the Jaizkibel as far as Arando-aundi and Arando-txiki, which mark the entrance to the port of Pasajes. It follows the edges of Mount Ulía with the cove of Mendiola and the Mompás point. Mompás and Igueldo, San Sebastián, with the Zurriola inlet, the mouth of the Urumea, Mount Urgull, the island of Santa Clara and the incomparable bay of La Concha. From Igueldo, it continues along the escarpments of Mendiotz, Tximistarri, Lurmandi, Burugan and Anarri to the Orio estuary. Here the river Oria, the most important river in Guipúzcoa, flows into the river Talaikoegia and Amesti. From Zarauz the coast slopes north, with the port of Guetaria and Cape San Antón. Then Zumaya, beach and harbour, to go back again and form the Deva inlet. It follows the town and port of Motrico and soon the beach of Saturrarán, in the jurisdiction of the latter, where the Biscayan coast begins, in front of the foothills of Mount Arno. From Txapitelako-arria to the Endara regatta at Endarlaza, the Bidasoa serves as the border Guipúzcoa and Navarre. Here it changes direction abruptly to the west and follows the Endara-erreka watercourse as far as the Aya crags (832 m). It turns south again until it reaches Biandiz mountain (840 m). From here it heads west following the course of a tributary of the Añarbe. Then, in a south-westerly direction, it follows the capricious and uneven course of the Añarbe from Artikutza. After the junction of the Añarbe and the Urumea, the boundary follows the Urumea River until near Pikoaga. It crosses the Urumea and runs along the eastern foothills of the Adarra to the south, as far as Mount Mandoegui (1,043 m.). From here it heads towards the Urto bridge over the Areso, a tributary of the Leizarán, on the Berástegui- Leiza road. It then heads south to Mount Uli (494 m). Here it heads slightly south-west through Elosua (965 m) and the Ilarrazu pass, crosses the Araxes river and climbs the Bedayo mountains to Irumugarrieta (1,426 m), in Aralar. As far as the Lizarrusti pass (615 m), the line continues along the Aralar mountain range, which now serves as a watershed the Cantabrian and Mediterranean slopes. It continues in a south-westerly direction via Txaraigorri (963 m) and Intxusburu (946 m). From the vicinity of Mount Atxu, the boundary line slopes more to the south-west, reaches the Etxegárate pass (751 m) and climbs Mount Arbarrain (1,116 m), the boundary Guipúzcoa, Navarre and Alava. It continues in the same direction until it reaches the vicinity of Aratz (1,442 m).
The Guipuzcoa-Alava divide continues from Aratz to the San Adrián entrance. Always in a general East-West direction, it continues along the same Cantabrian-Mediterranean watershed, through the Aránzazu and Elguea mountain ranges with Artia (1,173 m.), Zaraya mountain range and Arlabán pass (617 m.), already above Salinas de Léniz. Beyond Arlabán, the border Guipúzcoa and Alava forms an almost right angle, running northwards parallel to the River Deva, along Mount Jarindo (886 m), following the watershed of the Deva basin and those that run towards Villarreal and Aramayona. Near Galarza (Arechavaleta), the boundary turns westwards, crosses the river Aramayona and heads northwards to Besaide, where the boundaries of Guipúzcoa, Alava and Vizcaya meet. The boundary Guipúzcoa and Vizcaya, which starts at Besalde, continues through Udala (1022 m.), Kanpanzar pass (457 m.), and crosses the divide the basins of the Deva (G) and Ibaizábal (V) rivers. It forms a sinus that penetrates towards the east, then heads northwest through Intxorta (737 m.) to the Pagatza pass (462 m.) and continues through Reizabal, descends to Olarreaga and heads towards Mount Urko (791 m.) in the northern part of Eibar. Then, through the municipal district of Aguinaga (Eibar), it makes a big bend and suddenly changes course towards Mount Kalamúa (767 m). It continues along the peaks until it reaches the Urkaregui pass. From here, along the foothills of Mount Arno (612 m), the boundary follows the watershed to the Bay of Biscay Saturrarán (G) and Ondárroa (V).