## 3 Method
### Field Data Collection of Geological Mapping  
A handheld Android device with AoRGMAP (Supplement App S1) can be used for field data collection for geological mapping. The user interface of AoRGMAP is shown in Figure 4a. The buttons of _PRB_, _attitude_, _photo_, _sample_, _sketch_, and _fossil_ are listed on the top of the screen. The _GPS_ button is displayed in a floating window (Figure 4a), which can be used for positioning to obtain the localities of geological points and other features. It can be  
Figure 3: The conceptual pattern of the PRB model (modified from [39]). (**a**) The combination of \(\mathbf{P}\) points. (**b**) The two \(\mathbf{P}\) points connected by a \(\mathbf{R}\) line. (**c**) A simple combination of \(\mathbf{P}\), \(\mathbf{R}\), and \(\mathbf{B}\) elements. (**d**) PRB model represents the intersection of multiple geological units. (**e**) Life cycle of a \(\mathbf{P}\) point and encoding rules of \(\mathbf{R}\) and \(\mathbf{B}\) lines. \(\mathbf{P}\) points build the framework of the PRB model, and some important information (e.g., lithology, photos, attitude, structure, geological boundary, field route, etc.) from observations in the field is linked with the \(\mathbf{P}\) points. \(\mathbf{B}\) lines define the boundaries between geological bodies crossed by the survey route. \(\mathbf{R}\) lines record the geological survey track. Each \(\mathbf{R}\) line usually represents the geological unit that it goes through.  
hidden during data input to reduce distractions. Take the \(\mathbf{P}\) point as an example--clicking the \(\mathbf{P}\) button activates the interface (Figure 4b) for typing information in the field. All of the geological information (Table 1) can be collected in the field in a similar way.  
The properties in AoRGMAP can be classified into three types: numeric data, terminology, and unstructured data. The numeric data include ID numbers, coordinates, attitudes, and spatial information (e.g., distance and direction). The coordinates, attitude, and spatial information can be acquired using a digital compass and GPS-based techniques. The properties associated with geological terminology can be inputted by selecting the options provided by a dictionary of the geological units, rock names, and contact relations. The unstructured data include photos, audio, videos, text descriptions, and sketches. In the geological notes (Figure 4b), geologists can type the text to describe the geological features of outcrops. In the PRB system, the photo information depends on the \(\mathbf{P}\) points by sharing some key fields. To input photo information, the square icon (Figure 4a) should be clicked to activate the input interface, as shown in Figure 4b. In this interface, the PDA's camera can be used to take photos through the button commands. In this process, information  
Figure 4: The user interface of AoRGMAP. (**a**) the base map and main buttons for field data collection; (**b**) the properties contained in the \(\mathbf{P}\) point.  
about the camera orientation, photo number, coordinate, description, and affiliation can be added using automatic and manual methods. The photos taken in the field are stored in a specific folder and encoded automatically. Attitude, fossil, and sample information is also collected similarly in the field survey.  
AoRGMAP provides three ways to record field sketch maps: vector, grid, and photo. In the vector way, a geologist needs to draw points, polylines, and polygons on the screen to constitute the sketch. The grid method uses a brush to sketch on the grid screen. The width and color of the brush can be set according to requirements. In this way, the photo of geological outcrops can be input as a background for geological feature annotation. If the above methods cannot satisfy the needs, the geologist can also draw a sketch map in the paper and input a digital photo of the sketch into the system.