# Extraction of Visible Boundaries for Cadastral Mapping Based on UAV Imagery
## 1 Introduction  
Establishing a complete land cadastre and keeping it up-to-date is a contemporary challenge for many developing and developed countries, respectively [1; 2]. In this research, the distinction between 'developing' and 'developed' countries is considered from a land administration perspective. A developing country refers to a country with low cadastral coverage. A developed country refers to full coverage of a country's territory with defined cadastral land plot boundaries and associated land rights. According to the International Federation of Surveyors (FIG) and the World Bank, only one-quarter of people's land rights across the world are formally recognized by cadastral or other land recording systems [1]. Thus, in developing countries, initial efforts are directed to accelerating cadastral mapping as a basis for defining and recording land rights boundaries and formalizing land-related rights aiming to guarantee land tenure security [3; 4]. In developed countries, beyond the initial adjudication stage or establishment of a cadastre, another challenge is the maintenance of person-right-land relation attributes and keeping the cadastral systems up-to-date [5; 6]. In countries with a tradition and long history of developing a cadastral system, conventional ground-based cadastral surveying techniques and high positional accuracy of boundary surveying were required. Decades were needed to complete the process of cadastral surveying/mapping and registration [1; 6]. Although land cadastres were established, some of the cadastral systems could not be maintained, which led to outdated cadastral maps. Person-right-land relationship is complex and dynamic. Keeping the cadastral system up-to-date(continuous recording of person-right-land relation attributes, in any land related event, as close as possible to real-time) also requires a flexible and dynamic cadastral system [2; 7]. Proposed cadastral surveying techniques are mostly indirect ones rather than ground-based. Ground-based techniques are often argued as being time-consuming and labor intensive [1; 5; 8]. Emerging tools are mapping techniques based on remote sensing data, in particular, data acquired with sensors on Unmanned Aerial Vehicles (UAVs) [9; 10; 11; 12; 13; 14; 15; 16; 17; 18]. Cadastral maps are usually defined as a spatial representation of recorded land plot boundaries or other spatial units that the land rights concern [19]. In general, sensors on UAVs provide low-cost, efficient, and flexible high-resolution spatial data acquisition systems enabling the production of point clouds, Digital Surface Models (DSM) and orthoimages [20; 21]. In cadastral applications, UAVs have gained increasing popularity due to the high cadastral mapping potential in a different setting, in rural and urban areas, for developing and developed countries [22]. In addition, UAVs are used for both the creation and updating of cadastral maps [22]. In developing countries, UAV-based cadastral mapping usually serves as a tool for the creation of a formal cadastral system [11; 12; 13]. In developed countries, the case studies focus on the assessment of UAVs' data positional accuracy estimation and its conformity with local positional accuracy requirements aiming to use the UAV data for updating existing cadastral maps [14; 15; 16; 17; 18]. Here, updating in most cases refers to the comparison of two cadastral maps--one representing the database state, the other recently acquired data. The term updating can be used as a synonym for a \"revision\" of existing cadastral maps [23]. However, in all case studies reported in [22], cadastral boundaries are manually delineated. It is argued that a large number of cadastral boundaries are visible and coincide with natural or manmade physical object boundaries [2; 24; 25]. In the land administration domain, automatic extractions of visible cadastral boundaries have been a recent topic of investigation.