## 2 Literature Review
### Modular Location Problem  
Modularity is a strategy recognized by academia and the industry and plays an important role in the development of sustainable systems [26]. Modularity is also one of the newest concepts in location problems. One can classify the models which use the concept of modularity in two categories:  
(1) Modularity which happens in points. For instance, [PERSON] and [PERSON] [27] presented a multi-period facility location problem with modular capacity adjustments and flexible demand fulfillment. In their model, customers were divided according to their sensitivity to delivery lead times. They also proposed two mixed integer linear programming formulations and provided an extensive numerical study on randomly generated data with different demand patterns. More recently, [PERSON] and [PERSON] [28] addressed a modular facility location problem with application in the chemical industry in a way that modules assignment should be conducted considering the fact that one module product is necessary for the operation of the next module. In addition to this consideration, [PERSON] and [PERSON]'s model is capable of assigning modules with different capacities. [PERSON] et al. [29] studied a dynamic facility location problem with modular capacities as an extension of well-known location-allocation problem with capacity expansions possibilities that can be performed via a finite set of projects, and modules are represented as capacity blocks in facilities. As the problem is studied in a finite time horizon of discrete periods and module relocation costs are not considered, the modules can easily close in one facility and open in other one in each time period to optimize the objective demand points allocations.  
(2) Modularity that happens in arcs. [PERSON] et al. [30] presented two mixed integer programming formulations, a flow-based and a path-based formulation for the modular hub location problem. Their problem formulated the flow-dependent transportation costs using modular arc costs and then they compared the models using linear programming relaxation bounds. [PERSON] et al. [31] addressed a capacitated modular single assignment hub location problem having modular link capacities between nodes and hubs. They also solved the proposed model with an extension of existing neighborhood structures called a general variable neighborhood search. In a similar attempt, [PERSON] and [PERSON] [32] investigated the trade-offs between the stepwise cost function and its linear approximation for the modular hub location problem. The modularity in their work arose from the transportation costs depicted as a stepwise function of the number of vehicles that had a significant cost reduction, which could not be properly measured by using a simple linear cost function.  
According to the models described above, the MMCMCLP considers the modularity that happens in the arcs. There has not been any problem that focuses exclusively on modularity in maximal covering location problem. In addition, MMCMCLP is considered in a dynamic environment and capacitated facilities are located while their corresponding modules with suitable sizes are assigned to the facilities in each period.