The Irish band U2 could have written their song "Where the Streets Have No Name" about San José. Admittedly, some streets have names, but no one seems to know or use them. Streets in the center of the capital are laid out in a grid, with avenidas (avenues) running east and west, and calles (streets) north and south. Odd-number avenues increase in number north of Avenida Central; even-number avenues, south. Streets east of Calle Central have odd numbers; those to the west are even. Locals rarely use the numbers, however.
Costa Ricans rely instead on a charming and exasperating system of designating addresses by the distance from landmarks, as in "100 meters north and 50 meters west of the school." Another quirk: "100 meters" always refers to one city block, regardless of how long it actually is. Likewise, "200 meters" is two blocks, and so on. (As you can imagine, getting a pizza delivered here is quite a challenge.)
Historically, the reference point was the church, but these days it might be a bar, Burger King, or even a quirky landmark: the eastern suburb of San Pedro uses the higuerón, a prominent fig tree. The city has embarked on an ambitious project to name all its streets once and for all. Even after it’s completed, it's improbable that anybody will know or use the names. Your best bet is to follow the time-honored practice of ir y preguntar (keep walking and keep asking).