Simpson Thacher & Bartlett is advising Chinese e-commerce giant Alibaba Group Holdings Ltd. on a $1.58 billion proposal to buy Beijing-based digital mapping company AutoNavi Holdings Ltd.

Hangzhou-based Alibaba, which already owns 28 percent of AutoNavi, has offered to buy the remaining ordinary shares for $5.25 apiece. Nasdaq-listed AutoNavi offers digital map content and navigation solutions in China for mobile and Internet platforms.