Something which not only confused myself originally, but also is found in some population statistics of the Thai cities is to equal the capital district (อำเภอเมือง , Amphoe Mueang) of the provinces with the city of the same name. I first learned that this is a big misunderstanding when I got hinted to a post on skyscrapercity.com, where the largest cities of Thailand were listed and explained that the actual municipal (เทศบาลน, thesaban) areas is usually much smaller than that of the same-named district. This often leads to the claims that either Chiang Mai or Nakhon Ratchasima are the second-largest city of Thailand, while in fact it is with a large distance Nonthaburi (see the list of Wikipedia).
Probably one of the reasons for this misunderstanding is the fact that the local administration like in the municipalities and the central administration going down the ladder province, district, subdistrict and village exist in parallel. All of Thailand (except the capital Bangkok) is subdivided into the central administrative units, while only some parts belong to municipalities, which take over some of the tasks from the central administration - most notably the sanitation like garbage collection or waterworks.
Pictured above is the administration office of the township (thesaban tambon) Mae Sai in the far north of Thailand.