Improving the Accuracy of Article 14 Maps: With LRTK, Centimeter-Level Positioning Makes Boundary Surveying Reliable

The "Article 14 map," which accurately indicates land boundaries, is an official map kept at the Legal Affairs Bureau under Article 14 of the Real Estate Registration Act. The boundary points of each parcel are represented by coordinate values in the plane rectangular coordinate system, and the drawings are produced with a guaranteed level of accuracy so that, even if boundary markers are lost due to disasters or construction, the boundary can be restored on site from the map information. In other words, high on-site recoverability through high-precision surveying is crucial, and Article 14 maps that ensure the accuracy of area, distance, shape, and position serve as truly reliable documents indicating boundaries. However, at present only about 60% of the country has been covered, and in unprepared areas people must rely on old cadastral maps (plans equivalent to maps) created in the Meiji era. These old cadastral maps have low surveying accuracy and lack on-site recoverability, which can cause boundary disputes. Therefore, what will become increasingly important going forward is how to ensure high positioning accuracy when creating or updating Article 14 maps.

Challenges Faced in Boundary Surveys and Current-Condition Surveys

In practice, boundary determination and current-condition surveys face many challenges in ensuring accuracy and work efficiency. For example, when confirming or restoring boundaries between adjacent parcels, inaccuracies in the underlying documents can easily lead to discrepancies on site and prolong the time required to reach agreement on the cadastral boundary. In particular, in areas with confused cadastral maps, the positional relationships on paper do not match the actual land shape, requiring surveyors to re-measure on site from scratch to reconcile differences. Furthermore, when boundary markers are missing, restoration work relies on remaining markers or past survey maps, but small errors can accumulate and leave uncertainty about the boundary position.

The same applies to current-condition surveys: recording the land’s actual shape and the positions of structures in detail requires measuring a large number of points, which is arduous. Surveys are especially difficult in uneven terrain or densely wooded areas, and it can be impossible to obtain a sufficient number of survey points. Moreover, to draw survey results and make them consistent with the registry’s installed maps (Article 14 maps) requires advanced accuracy management and data processing. Surveyors must carefully verify whether the measured point clouds and coordinates match existing coordinate systems and control points, and may need additional surveying or corrections. These tasks consume time and effort and carry a risk of human error. To perform boundary surveys quickly and accurately with limited personnel, efficiency gains from new technologies are indispensable.

Limits of Conventional Surveying Methods (TS・GNSS) in Ensuring Accuracy

Traditional mainstays of boundary surveying—total stations (TS) and conventional GNSS surveying instruments—each have advantages and limitations. TS can measure distances and angles with millimeter-level precision and is highly reliable for short-range relative measurements. However, the drawback is that operation requires manpower and time. Heavy equipment must be transported and set up on site, and typically two or more people are needed: one to operate the instrument and another to hold the prism at each point. When terrain is uneven or obstacles exist, the instrument must be repositioned as needed, and care must be taken to maintain line-of-sight between survey points. In addition, to tie TS-derived coordinates to a public coordinate system requires linking to known points or performing network surveys with multiple points; a single TS setup cannot by itself produce absolute coordinates. Regular calibration and maintenance of the equipment are necessary, and handling requires advanced expertise.

On the other hand, GNSS positioning represented by GPS has the advantage of acquiring coordinates over wide areas with fewer line-of-sight constraints because it uses satellites. However, single-point standalone positioning typically has large errors of about 5–10 m (16.4-32.8 ft), making it unusable for boundary measurement. High precision requires techniques such as RTK (Real-Time Kinematic) or static positioning. When performing RTK with conventional GNSS equipment, a base station (reference receiver) and a rover (mobile receiver) must be prepared, and corrections are sent via radio or mobile communications during positioning. This also involved considerable effort. If one sets up a private base station, its positioning and communication setup are required; even when using wide-area network RTK services, conditions such as being within a communication area and paying monthly service fees apply. Moreover, conventional GNSS units, including antenna and battery, were large and heavy, making them as cumbersome to carry as a total station. Satellite signal reception is unstable under forests or in the shadow of buildings, and it was often necessary to wait a long time to obtain a fixed solution (cm-level fix). In short, conventional methods that sought both accuracy and immediacy incurred high personnel and material costs.

How LRTK Achieves Centimeter-Level Positioning and Its Stability

A new technology that has emerged in this context is LRTK. LRTK (Lightweight RTK) is a GNSS real-time positioning system that works with smartphones and can provide centimeter-level positioning results immediately on site. Its mechanism is to apply correction data in real time to the GNSS satellite signals to improve accuracy. Specifically, radio signals from multiple satellite navigation systems (not only GPS but also GLONASS, Galileo, and the QZSS Michibiki) are received by a high-sensitivity small antenna, and correction information counteracts error factors such as satellite clock errors, ionospheric delays, and tropospheric delays. As a result, positioning errors that were normally several meters are reduced at once to the range of about 1–2 cm (0.4-0.8 in), (about 3 cm (1.2 in) in the vertical direction). Correction information can be received via RTK reference station services over mobile networks, and LRTK also supports Japan’s QZSS Michibiki-provided centimeter-level augmentation service (CLAS), allowing direct reception of high-precision corrections from satellites even in mountain areas where mobile communications are out of range.

A key feature of LRTK systems is that high-precision positioning can be realized very easily. Using a dedicated small GNSS receiver (a device roughly the same size as a smartphone and weighing about 165 g), attach it to an iPhone or another smartphone and launch the app to begin surveying solo. If the smartphone is mounted on a pole with an antenna (monopod) and leveled with a bubble level, point observations that previously required two people can be handled by one person with ease. During positioning, the app visualizes current accuracy and satellite acquisition status so you can see at a glance whether a fixed solution has been achieved. If errors are large, accuracy can be improved by using the function that automatically averages multiple measurements at each point. In fact, averaging 60 positionings at a point with LRTK produced horizontal accuracy of about 8 mm (0.31 in). Thanks to advanced positioning algorithms and the synergistic effect of multi-GNSS, LRTK’s strength is that it can maintain centimeter-level accuracy stably even while moving. Each measured point immediately provides not only geodetic latitude, longitude, and ellipsoidal height but also coordinates in Japan’s plane rectangular coordinate system, enabling on-the-spot plotting onto maps and drawings. Combined with the lightweight, compact equipment, this offers an innovative mechanism for “precise positioning anytime, anywhere.”

Accuracy Management via AR Navigation, Point-Cloud Measurement, and Cloud Sharing

LRTK does more than just measure point coordinates; it includes various functions that support on-site work and deliverables end to end. A prime example is AR-based coordinate navigation. The dedicated app can overlay predefined target points and boundary lines on the camera view, allowing invisible boundaries on site to be understood intuitively. For example, if you know the coordinates of a boundary point you want to restore, simply point the smartphone and approach the AR-displayed marker to identify the stake position within a few centimeters of error. Tasks that used to be done by following angles and distances with surveying instruments while indicating “this is the boundary point” are now carried out visually and smoothly via AR guidance. When placing multiple points in sequence, the site can be reproduced according to the layout on the map, so misalignments with adjacent land or deviations from straight lines become apparent on the spot. AR that seamlessly links drawings and the field is powerful not only for boundary restoration but also for stake setting based on design drawings and for as-built inspections (verifying that construction has been carried out as designed).

Next is 3D point-cloud recording. LRTK systems can use a smartphone’s LiDAR scanner and other sensors to scan the surrounding terrain and structures, obtaining high-density point-cloud data. These point clouds are of course tagged with global coordinates (latitude, longitude, elevation, and plane coordinates), so a three-dimensional model of the terrain is available immediately. For example, if you record the ground around a boundary and the positions of adjacent buildings as point clouds, you can later analyze positional discrepancies with the boundary line in detail in the office, and measure elevation differences and structure heights. You can also calculate earthwork volumes for a specific area from the point cloud or generate heat-map-style difference analyses against design models instantly. Tasks that previously required specialized 3D laser scanners or drone photogrammetry can now be completed with a single smartphone. If you want to improve acquisition accuracy, you can load known points or boundary markers as control points into the point cloud and use coordinate-based alignment (georeferencing). This reduces overall error even for wide-area point clouds, enabling accuracy management comparable to public surveying standards.

Cloud sharing is also an important element of LRTK. Measured coordinate data, photos, and point clouds can be synced and saved to the cloud on site, eliminating the need for cumbersome data processing back at the office. On the cloud, you can check each survey point’s position and attributes on a map screen, and by issuing a shareable URL you can instantly share results with stakeholders. For example, if a land and building surveyor records the situation at a boundary meeting with positioning photos and uploads them to the cloud, colleagues waiting at the office can check in real time and provide guidance. Data are automatically backed up, so even if equipment is lost or damaged on site, the survey results are safely preserved. It is also easy to retrieve past survey data from the cloud for reference, so you can compare multiple surveys conducted over time to capture land changes. Compared to the era of handing over paper maps or USB memory sticks, the ability to quickly and reliably manage and share deliverables including accuracy information is a major advantage well suited to modern surveying work.

Accuracy Validation Examples and Use Cases in Boundary Surveying

The accuracy of LRTK has been demonstrated through various validations. One example reported is a test in which LRTK positioning was performed at a known point assumed to be a first-order control point (a national reference point) and the coordinates were compared with those obtained by another high-precision GNSS instrument. The results showed differences of a few millimeters or less in both horizontal and vertical directions, confirming accuracy comparable to conventional high-cost surveying equipment. In another case where about ten boundary markers were measured consecutively, the relative errors among points were within 1 cm (0.4 in), and averaging multiple measurements improved the maximum error to about 5 mm (0.20 in). These accuracy validations suggest that LRTK can sufficiently meet the level required for Article 14 maps—namely, that boundaries can be restored on site within a certain error range.

Practical use cases are diverse. For measuring boundary points, LRTK can rapidly acquire coordinates of each cadastral point. Steps that formerly involved traverse surveys with TS and subsequent calculations can now be skipped because plane rectangular coordinates can be obtained directly on site, enabling immediate drafting. Measured points can be provided directly to the registry as coordinate data for Article 14 maps, reducing later coordinate transformation and adjustment work. During surveying, the straightness or corner angles of a boundary line can be checked on the app screen, allowing verification at each stage that points are in ideal positions. If existing boundary markers differ from old cadastral maps, the magnitude of the discrepancy can be quantified immediately, making it easier to explain the situation to stakeholders during meetings.

LRTK also provides confidence for boundary marker restoration and installation. When restoring a lost boundary marker, enter the precomputed coordinates into the app and the AR navigation will guide you to the installation position on site. There is no need to rely on experience and intuition with tapes or rods to estimate positions; markers can be embedded accurately in a short time. After installation, you can re-measure the point with LRTK to confirm at a tap that the coordinate matches the planned value. This allows you to retain evidence that the restored marker falls within the prescribed error range. If boundary disputes arise later, you can present the positioning data and photos stored in the cloud as objective documentation.

LRTK is also powerful for current-condition surveys and drawing reconciliation. For example, in cases of residential land development or land subdivision, it is necessary to accurately capture not only boundary lines but also the positions of existing structures (fences, buildings) and terrain variations. By measuring boundary points with LRTK while simultaneously scanning the surface for point clouds, you obtain comprehensive “as-built” data for the site. From the acquired point cloud you can create an overall current-condition map and overlay design drawings or cadastral boundary lines from the registry to instantly identify discrepancies between design and reality. If a fence encroaches, the distance can be calculated precisely; conversely, if a building is far from the boundary line, you can consider whether land use is inefficient. In this way, LRTK’s positioning and point-cloud technologies support multifaceted current-condition understanding rooted in boundary lines.

There are also administrative and public-survey use cases, such as emergency surveying immediately after disasters. In areas where many boundary markers have been broken or washed away by earthquakes or landslides, if Article 14 maps have been prepared the coordinates of lost boundaries remain. LRTK can position even when communications infrastructure is disrupted as long as power is available, and it has begun to be adopted for rapid boundary restoration and terrain surveying in disaster-stricken areas. For example, LRTK was used after the Noto Peninsula earthquake to record and share damage along evacuation routes using the positioning-photo function. The mobility that enables reliable spatial information to be recorded in previously difficult situations is proving valuable beyond the confines of boundary surveying.

Benefits of Adoption: Reduced Workload and Increased Deliverable Reliability

From the technical features and practical examples described above, many benefits of adopting LRTK become clear. First is the significant reduction in workload. Surveys that previously required two skilled personnel can be completed by one person, reducing labor costs and allowing more flexible scheduling. The physical burden of carrying heavy equipment over long distances disappears, reducing on-site physical stress. Setup and teardown time are shortened, increasing the amount of work that can be completed in a day. Particularly for wide-area cadastral identification tasks or current-condition surveys requiring many points, dramatic efficiency improvements compared to conventional methods are expected.

Improved drawing consistency is another key benefit. Coordinates obtained with LRTK are natively values on a public coordinate system, so errors and mistakes that can occur when converting to another coordinate system in postprocessing are avoided. Results from adjacent sites are less likely to conflict, resolving problems where stitched maps do not align. This makes it easier to secure a higher accuracy classification for maps filed at the Legal Affairs Bureau. When land area is calculated from boundary point coordinates, increased trust in that accuracy can also facilitate consensus among stakeholders.

Regarding improved reliability of deliverables, digital data provide objectivity and reproducibility. Points acquired with LRTK are recorded to the cloud with date, time, and accuracy information, leaving little room for arbitrary tampering or subjective interpretation. Sharing on-site measurements at boundary meetings helps landowners feel confident in the results. If doubts arise later about whether the correct location was measured, the recorded data can be verified by a third party. In this way, transparent surveying contributes to improving trust relationships related to land boundaries. Height information, which is hard to convey on paper, can also be supplemented by 3D point clouds, greatly enhancing explanatory power by presenting terrain and boundary conditions in three dimensions. This is useful in registration or boundary dispute mediation, where deliverables backed by accurate data provide reassurance to all parties.

Conclusion: Everyday Use and the Potential Opened by LRTK

LRTK offers a groundbreaking solution to the twin challenges of ensuring accuracy and improving efficiency in the creation and maintenance of Article 14 maps. By combining the stability of centimeter-level GNSS positioning with advanced functions such as AR, point clouds, and cloud services, LRTK enables consistent accuracy management from the field to deliverable production. Its benefits are not limited to official surveying work performed by licensed land and building surveyors or survey engineers. With its ease of use and immediacy, LRTK also holds potential for routine simple surveys and periodic field records.

For example, LRTK’s high accuracy can be applied to quick checks of adjacent boundary positions during surveying breaks or to repeated fixed-point observations of ground subsidence before and after construction—small everyday measurements that previously might have been omitted can now be recorded accurately, reducing later regrets of “I should have measured that.” Easy cloud-based data management also enables accumulated surveying data to be used in GIS-like ways for land management and new initiatives. As precise positioning that was once expensive and difficult to handle becomes accessible to anyone, the very style of surveying is changing.

LRTK, which dramatically improves the reliability and efficiency of boundary surveying, will surely contribute to enhancing the accuracy of Article 14 maps while broadening the scope of surveying work. As mobile high-precision positioning technologies like this become more widespread, more land parcels will have accurately determined cadastral boundaries, smoothing registration practices and land use. By adopting LRTK’s combination of accuracy and convenience, boundary surveying can be freed from previous constraints and new possibilities can be opened. For the sake of on-site reassurance and improved reliability, consider actively incorporating such advanced tools.