[HansTWN]

The Hanzi are the same everywhere -- but they are not connected to Mandarin. So "Mandarin Hanzi" is a misnomer, it must be "Chinese Hanzi" (since the Han 漢 actually stands for the Han people that is, of course, repetitive). Mandarin really is only the dialect of the Beijing/Tianjin region. Hanzi are covering all of China. Hanzi were historically the only way to communicate for Chinese from different regions, before Mandarin was taught in schools all over the country. Every character is pronounced differently by a Cantonese speaker than the same character is pronounced by a Mandarin speaker, but the meaning is the same (quite often there are similarities in pronunciation but not always). Chinese characters are symbols, and every Chinese dialect/language affixes a different pronounciation to each character. Every Chinese can read 一 二 三 and knows it means 1,2,3. But in Mandarin it will be pronounced "Yi Er San"; in Cantonese "Yat Yi Sam" and in Hokklo/Taiwanese "Ji Neng Sa". In writing all 3 languages are mostly the same, except for some of the differences I pointed out. Remember, the characters are not phonetic symbols.

People in Hong Kong have created a number of special characters that only they use to cover some local expressions. Some grammatical constructions are different. So if a Mandarin speaker reads a HK newspaper he/she has no problems understanding it, it just may seem a little strange sometimes. Because the paper will be written "in Cantonese".

Some Chinese dialects actually only are dialects (take Sichuanese, for example). The pronounciation is a little off. The tones differ sometimes, they have some unique local vocabulary, but a Mandarin speaker will do fine. After a day or two in the region you can get almost everything when overhearing locals' conversations.