Germany’s big-three premium-brand auto makers are preparing to launch a formal bid to acquire a majority stake in Nokia Corp.’s Here mapping unit, in a consortium that includes Chinese technology group Baidu Inc. and values Here at “considerably more than €2 billion,” according to people familiar with the situation.

BMW AG, Audi AG, and Daimler AG’s Mercedes-Benz are usually fierce rivals in the market for luxury automobiles. But they are so worried about Silicon Valley’s ambitions that they are banding together to acquire...