Because the Mandarin pronunciation of Shaanxi and its eastern neighbour Shanxi differs only in tone, their spelling in pinyin romanization differs only by tone marks ("Shǎnxī" and "Shānxī", respectively). The People's Republic of China therefore adopted the special official spelling "Shaanxi". The first syllable is derived from Gwoyeu Romatzyh romanization, which reflects the tones of the words' vowels in their spelling. Before the adoption of pinyin, Shaanxi was romanized as Shensi in the Chinese postal romanization scheme. When tone marks are noted, it is spelled "Shǎnxī" rather than "Shǎanxī" or "Shaǎnxī".