Pompeii is the only ancient city whose geographic layout is known precisely and without subsequent alterations. Its layout did not follow a regular structure typical of Roman cities due to the irregular characteristics of the terrain. However, its streets were straight and formed a grid following the traditional Roman style, with its main road (cardo) and two transversal roads (decumanos). The southwestern sector, on the other hand, showed a more irregular design and constituted the original core of the Oscan settlement. Over time, several extensions were made with more regular layouts. The layout of the walls was already established in the 6th century BC and, most probably, that of the main streets. However, even in 79 A.D., there were areas in the city, especially in the eastern sector, that remained undeveloped, including wastelands and cultivated areas, indicating that the population density within the walls was never very high.

The current names of the streets and gates of the city mostly date back to the 18th and 19th centuries, since the original names, if they had them in Roman times, have not been preserved. According to an inscription, today's Via Stabiana was probably called Via Pompeiana. The same inscription refers to a Via Iovia and Via Dequviaris that have not yet been identified. As for the gates, the present Porta Herculanensis, known as the Herculaneum Gate, bore the name Porta Salis or Saliniensis, the Salt Gate, in reference to the salt mines near the gate. The Porta Marina, Gate of the Sea, was probably called Porta Forensis, Gate of the Forum, because of its proximity to the city's forum.

Today, a system developed by Giuseppe Fiorelli is used to locate the buildings on the city map. This system divided Pompeii into nine regions, and assigned an identifying number to each block and, within each block, to each gate.