## 1 Introduction
From the perspective of China's engineering construction method, a unit can be divided into contractor units, construction units, and government units. In this study, contractor units refer to the outsourcing units who are responsible for BIM-related content in the project construction process; the construction units refer to owners and units who have contractual relationships with the contractor units; the government units are responsible for Geographic Information Systems (GIS)-related content in urban regional planning and project administrations, as shown in Figure 1. In the current practice, contractor units are responsible for individual projects, construction units are responsible for group projects, and government units are responsible for regional projects [5; 6]. Each unit is managed and entrusted through paper materials (report, drawing, etc.) or communication equipment (mail, telephone, etc.). Such traditional methods can easily cause information backflows and work duplications [7; 8]. Hence, it is difficult to meet the integration and refinement requirements of the multi-unit collaborative management of construction project information. In this paper, according to the size of the project scope, the project scope is divided into three scales (microscale, mesoscale, and macroscale) (scale is a standard that divides variables (social phenomena) into categories or levels). Individual projects in charge of contractor units are regarded as the microscale, group projects in charge of construction units are regarded as the mesoscale, and regional projects in charge of government units are regarded as the macroscale [9]. In the process of engineering construction, various information needs are transmitted among different scales. For example, micro-meso (referring to the business involved in the transition from microscale to mesoscale) information includes information about the interior of the building (e.g., wall type, room area, etc. ), and meso-macro (referring to the business involved in the transition from mesoscale to macroscale) information includes information outside the building (e.g., boundary line of land, plot ratio, etc.). Challenges exist in the process of information collaboration among different scales, as shown in Figure 2.  
The overall goal of this study is to provide theoretical and practical support for effective information collaboration in the construction of smart cities using BIM. Previous studies have examined information management methods at three scales, respectively, for individual projects, group projects, and regional projects [10]. However, the project information among the three scales is still scattered, and a complete theoretical method has not been formed. It is crucial to formulate a method for combining the three scales systematically and truly achieving an effective collaboration. This study proposed a collaborative management method for multi-scale information using BIM. When BIM is applied in a project, information is encapsulated in the model. Extracting valid management and control (M&C) data from the model database is the key to information collaboration. And the management protocol ensures the smooth application of BIM in the project. Hence, the proposed method examined information management from the three perspectives of model, data, and management. In this way, a multi-party collaborative and shared engineering data center could be formed to strengthen the communication efficiency among different units, reducing the complicated and redundant work content of relevant departments. Finally, the proposed method realizes the overall collaborative control of  
Figure 1: The division of three scales. Figure 2: Analysis of problems between scales. project information among multiple units and satisfies the vision of resource sharing of project information. The rest of this paper is organized as follows: The second section presents a systematic literature review of BIM and information management (Section 2).