San Sebastián has an area of 4.01 km2[3] and an elevation of 1,125 metres.

[1] It shares its southern border with San José Province's Alajuelita and Desamparados cantons.

[4] For the 2011 census, San Sebastián had a population of 40,065 inhabitants.

[7] San Sebastián District includes the "barrios" (or neighbourhoods) of Bajos Canada, Bengala, Bilbao, Cañada Sur, Carmen, Cascajal, Cerro Azul, Colombari, Colonia Kennedy, Guacamaya, Hogar Propio, Jazmin, Lopez Mateo, Los Geranios, Los Olivos, Luna Park, Mojados, Mojito, Parque de La Paz, Paso Ancho, Pavi, Presidentes, San Gerardo, San Martín, San Sebastián, Santa Rosa, Santo Domingo Sabio, Seminario, Galenos, Umará and Zorobarú.

The district is covered by the following road routes: