# Optimized Travel Itineraries: Combining Mandatory Visits and Personalized Activities
## 1 Introduction  
Tourism refers to the activity of traveling to and staying in places outside one's usual environment for leisure, business, or other purposes. It encompasses the services and industries that cater to travelers, including transportation, accommodations, food and beverage, entertainment, and attractions. Tourism can be domestic, where travelers explore their own country, or international, where they visit foreign destinations. Industry plays a significant role in the global economy, providing jobs and generating revenue for local communities [1, 2]. Recently, independent travel has grown in popularity, especially among youths. Independent tourists do not follow only the common touristy places and use pre-defined travel packages but seek more adventures. They choose the unconventional routes,experience other cultures, seek adventure in a wide variety of environments, learn about foreign places, and plan excursions independently. These travelers favor custom travel plans over the usual tour packages offered by travel agencies [3]. Consequently, online travel information is highly beneficial for tourists organizing their own trips. However, this process is quite complex as collecting information and assessing travel itineraries demands a significant amount of time and effort [4; 5; 6]. Additionally, the conflicting objectives of tourists, due to their individual interests, make planning even more challenging [7]. This issue is known as the \"tourist trip design problem\" (TTDP), which involves creating tour routes for tourists to maximize their satisfaction while adhering to numerous constraints [8; 9]. Tourists that visit an area for a short period are unable to see every location available due to time and budget constraints. Tourists need to choose what they consider to be the most valuable Points of Interest (POI) [10]. Travelers might not have difficulty aside from scheduling their own itineraries. However, group travelers might need to compromise with their preference, especially in the large urban areas with many POIs. They need to determine sequences of POIs during a specific period to be included in the plan and determine modes of transportation systems [11]. Nowadays, although tourists are comfortably planning their trips using the information available on the website, they still need the trip plan advisory services. As a result, there are numerous platforms addressing the tour planning problem, aiming to design a trip that includes the maximum number of POIs while staying within various budget and time constraints [12]. Some of the examples of these platforms include Personalized electronic tourist guides (PETs), Recommender Systems (RSs), TRIPBUILDER, and eCOMPASS. Each of these platforms uses different models to create personalized routes. PETs are a platform that determines the profile of the tourist and their restrictions. Combining this information with knowledge about local attractions, PETs provide a personalized route for the tourists [13]. This platform is available on mobile hand-held devices [14]. RSs are among platforms that have been widely used to manage the information overload and provide travel recommendations to tourists. These systems are tailored for mobile device users and offer a significant enhancement to tourist experiences by recommending diverse multimedia content, context-aware services, and reviews ratings from other users, among other features [15]. TRIPBUILDER is a framework designed for creating personalized sightseeing tours in cities. It models the task as a Generalized Maximum Coverage (GMC) problem, aiming to maximize the measure of personal interest based on the user's preferences and time budget for visiting [16]. Another example is eCOMPASS, an application available on both websites and mobile devices. eCOMPASS creates personalized multimodal tours based on chosen urban attractions and is unique as it is the only commercial tour planner that helps tourists navigate using public transit [17].