###### Abstract  
In recent years, different types of monitoring systems have been designed for various applications, in order to turn the urban environments into smart cities. Most of these systems consist of wireless sensor networks (WSNs), and the designing of these systems has faced many problems. The first and most important problem is sensor node deployment. The main function of WSNs is to gather the required information, process it, and send it to remote places. A large number of sensor nodes were deployed in the monitored area, so finding the best deployment algorithm that achieves maximum coverage and connectivity with the minimum number of sensor nodes is the significant point of the research. This paper provides a systematic mapping study that includes the latest recent studies, which are focused on solving the deployment problem using optimization algorithms, especially heuristic and meta-heuristic algorithms in the period (2015-2022). It was found that 35% of these studies updated the swarm optimization algorithms to solve the deployment problem. This paper will be helpful for the practitioners and researchers, in order to work out new algorithms and seek objectives for the sensor deployment. A comparison table is provided, and the basic concepts of a smart city and WSNs are presented. Finally, an overview of the challenges and open issues are illustrated. s 2022222002222002222200222222002  
to meet countries' goals in increasing surveillance, intelligence, and reconnaissance in many safety-critical applications, where the IoT will also have an important role. Though designing WSN many challenges can appear in the form of deployment, localization, communication, data gathering, coverage, and tracking, the most important issue that we focus on here in this research is the deployment problem, which is the first major challenge in designing a WSN monitoring system for a smart application. **Motivations:** Most of the research in the literature focused on the deployment problem of WSNs in general. Based on the idea of monitoring large and open spaces, on the other hand, very few studies have been conducted regarding this problem in smart cities for reasons that are listed as follows [2]:  
* The monitored area: some areas are large and require a network structure, such as water distribution networks, transportation networks, and streetlight networks. Some areas required three-dimensional (3D) monitoring, such as the structural health monitoring of bridges and towers. * Different types of sensor nodes for the same measurements: static inductive loops or static cameras, for example, can be used to measure the traffic volume on the roads. * Densely deployed sensor network in the monitored area: different sensor nodes for different applications exist in the same monitoring area. Due to these reasons, some challenges have appeared, which affect the process of sensing in smart city monitoring systems, the most significant of which is the deployment of sensor nodes, which is limited by the monitored area's structure, that is, what kind of sensor nodes are required and where they should be deployed to satisfy the best coverage, connectivity, and cost-effective monitoring. **Contributions:** This research study presents a systematic mapping study that will focus on the node deployment problem for smart city monitoring systems over the period 2015-2022 by using meta-heuristic optimization algorithms. Therefore, this research aims to answer the research questions that are related to this problem and, in that way, could be helpful for researchers and practitioners/developers to better understand the deploy  
Figure 1: Smart city applications [1]. ment problem in that field. This will facilitate finding new solutions and adding further contributions to its development. This paper is organized as follows: Section 2 describes the background of infrastructures and technologies that support the smart city and WSN, as well as the preliminaries of WSN deployment.