Sử dụng dữ liệu vector cho phép bản đồ được chia thành các lớp riêng biệt, mỗi lớp có thể được tiếp tục bị phân hủy thành các tính năng cá nhân. Người sử dụng có quyền tự do của trình duyệt bản đồ di động bằng cách thực hiện bất kỳ hành động bản đồ được mô tả trong Bảng | 10 Designing Interactions for Navigation in 3D Mobile Maps 211 use of prior knowledge and 4 transforming the locus of task processing from working memory to perceptual modules. However if guidance was optimally effective one could argue that users would not need to relapse to epistemic action and other corrective behaviours. This we believe is not the case. Because of substantial individual differences in representing the environment and in the use of cues and landmarks . Waller 1999 and because information needs vary between situations the best solutions are those that support flexible switches between efficient strategies. Manoeuvring in a VE can be realised with various levels of control over movement. Table presents a set of manoeuvring classes in decreasing order of navigation freedom. Beyond simply mapping controls to explicit manoeuvring one can apply metaphors in order to create higher-level interaction schemes. Research on virtual environments has provided several metaphors see Stuart 1996 . Many but not all of them are applicable to mobile 3D maps partly due to restrictions of the input methods and partly due to the limited capacities of the user. Several methods exist for assisting or constraining manoeuvring for guiding the user s attention or for offloading unnecessary micro-manoeuvring. For certain situations pre-animated navigation sequences can be launched via shortcuts. With external navigation technologies manoeuvring can be completely automatic. It is essential that the special circumstances and potential error sources typical to mobile maps are taken into consideration in navigation design. Selecting a navigation scheme or metaphor may also involve striking a balance between support for direct search for the target pragmatic action on the one hand and updating cognitive maps of the area epistemic action on the other. In what follows several designs are presented analysed and elaborated in the framework of navigation stages Downs and Stea
