Located immediately west of Tehran, Karaj functions as both an extension and a buffer of the capital. Its position at the Alborz foothills places it on critical transport, industrial, and security axes radiating from Tehran.

Karaj’s growth accelerated during the late 20th century as Tehran expanded beyond its administrative limits. Industrial zones, housing overflow, and research facilities concentrated here, embedding Karaj into Iran’s core power geography.

Karaj was a minor settlement along the routes west of Tehran until Pahlavi-era planning transformed it into a major industrial and residential centre. Deliberate policies to disperse industry from Tehran, combined with access to water from the Karaj River and reservoir, drove rapid growth from the 1950s onward.

After 1979 migration from rural areas accelerated expansion further and the population grew to several million, making Karaj one of the largest cities in Iran. In 2010 it was made the capital of the newly created Alborz province, formalising its status as an independent metropolitan centre, though functionally it has merged with Tehran into a single continuous conurbation.

Today Karaj hosts heavy and light industry, research institutes, military-linked facilities, and dense commuter populations. Its proximity to Tehran gives it elevated relevance in internal security planning, infrastructure resilience, and regime stability calculations.