San Juan is the most populous city and the most densely populated metropolitan area throughout Puerto Rico.  The population, however, has experienced a decline in recent decades as the population has scattered to the adjacent municipalities.

From 1899 to 1950 the municipality of San Juan did not yet include the municipality of Rio Piedras.  Thus, during this period the data regarding population, land area and population density only refers to the neighborhoods of Old San Juan and Santurce.

The former municipality of Rio Piedras, joined to San Juan in 1951, was the third most populous city of Puerto Rico at the time of annexation.  South of the capital, it was a strategic location that served as a meeting point for all the main roads on the island and as a prelude to the geography of San Juan.  This was just one factor that prompted San Juan’s dramatic urban development during the twentieth century.

Geography

San Juan is located in the northeast region of the coastal plains, north of Aguas Buenas and Caguas, east of Bayamon and Guaynabo, and west of Carolina and Trujillo Alto.

Old San Juan occupies the western shore of a rocky islet at the mouth of the Bay of San Juan.  During the twentieth century, major population centers emerged beyond the walls of the old city and the main island, and joined with existing groups in the south and east of Old San Juan.  During this period, San Juan saw a broader increase in population than observed in any region throughout Puerto Rico.  As a result, the city is now composed of a variety of neighborhoods or districts.

Districts

Old San Juan

Currently, the Municipality of San Juan is composed of eighteen districts.  One of these is the Old San Juan district, comprising the Isleta de San Juan, which was first established within this municipality in the year 1521.  By then the town had a land area of approximately 2.6 km².  Subsequently in 1863 the capital annexed its first suburb, known as Santurce, making the territory of the capital increase by more than 600% to 16.2 km². This district was part of then diluted San Mateo de Crabs. The other districts of San Mateo, meaning those of Hato Rey and Crabs were divided between the municipalities of Carolina and Rio Piedras.

To the east of Old San Juan district lies what was, under the Spanish colonial period, the County of San Jose de Santurce.  The area is full of hotels and condominiums lying on land that used to be owned by Paul Ubarri Y Capetillo, a Spanish manufacturer of railways.  The beaches and the Ocean Park of Puerto Rico are popular, and swimmers, surfers and kitesurfers can be seen along the Atlantic coast of the district.

Near Condado are two separate shopping areas, Santurce and Miramar.  Miramar is mainly a residential area located south of Lake County and it includes the old district of Miraflores and that of Platanal.  It drains into a landfill near where the first airport in Puerto Rico, Isla Grande Airport (or Airport Fernando Luis Ribas Dominicci) was built.  The Convention Center of Puerto Rico is in Miramar, along with piers for the ships at the Port of San Juan.

Santurce, originally named “San Mateo de Crabs” was the destination for freed African slaves during the early days of the city.  After that, Paul Ubarri requested permission to unite Santurce with San Juan via a tram route in 1878.  The main town was thus united with the city and renamed using the Spanish language Santurce (Santurtzi in Basque). Santurce is in the Museo de Arte de Puerto Rico.

South of Santurce is one of the oldest neighborhoods, Hato Rey.  Around the sixteenth century the neighborhood was the breeding ground for the cattle of the Royal Government (hence its name “the herd of the King”).  Hato Rey is currently considered the financial center of the island.  A section of this district is referred to as the “Golden Mile” (actually 0.47 miles in length), given in part to the large number of banks and companies located there.

In the southern part of the city is the mostly residential area of Rio Piedras. Rio Piedras used to be a separate city, founded in the mid-1850s, where there were sugar plantations and properties of some of the wealthier inhabitants of San Juan.  Of course, the staff, the working class also lived in the area.

The Spanish colonial governors also had their summer homes in the area of Rio Piedras, which eventually gave way to the main campus of the University of Puerto Rico. In 1951 the municipalities of San Juan and Rio Piedras were united to establish the perimeter of today’s San Juan. Today, Rio Piedras is the traditional home of the famous Market Square and includes the largest area of the municipality of San Juan.

The last major expansion of San Juan took place in the years 1951 through 1977.  The expansion was the result of legislation that was drafted, a product of which was the referendum promoted by the governor, Luis Muñoz Marin, to annex the city of Rio Piedras to the Municipality of San Juan.  In this way the territory of the capital increased to 107.6 km², bringing it near to its present size of 123.9 km².  This amounted to a growth of 765%.