Before we get too far along, it's useful to understand just what an embassy is, and the role of diplomatic personnel in conducting foreign affairs, and the other activities.
There are more than 170 foreign embassies in Washington D.C. As a rule, embassies are located in capitals, while other diplomatic facilities - consulates, trade missions, etc. - are found outside of Washington. Some countries have a sizable number of diplomatic offices in the U.S.; Mexico has more than 40 consulates throughout the country.
Each country's embassy in Washington is also usually a collection of several facilities, sometimes widely scattered in multiple locations. An embassy "residence" is the ambassador's official home, while the "chancery" is where diplomats' offices are located. Other facilities might include a separate office for military attaches, or for consular operations.