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

The "Article 14 map" that 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 (lot) are represented by coordinate values in the plane rectangular coordinate system, and the drawings are required to ensure a certain level of accuracy so that boundaries can be restored on site even if boundary markers are lost due to disasters or construction. In other words, on-site restorability achieved by high-precision surveying is crucial, and an Article 14 map that guarantees accuracy in area, distance, shape, and position becomes a reliable record that indicates the true boundary. However, at present only about 60% of the country has been covered, and in unprepared areas one must rely on old Meiji-era public maps (maps equivalent to cadastral plans). These old public maps have low surveying accuracy and lack on-site restorability, which can lead to boundary disputes. Therefore, ensuring how to secure high positioning accuracy when creating or updating Article 14 maps will become increasingly important.

Challenges Faced in Boundary Surveys and As-Built Surveys

In practical boundary determination and as-built surveying, there are many challenges regarding accuracy assurance and work efficiency. For example, when confirming or restoring boundaries between adjacent properties, if the underlying documents are inaccurate, discrepancies are likely to occur on site and it can take time to form agreement on parcel boundaries. In areas where public maps are confused, the positional relationships on paper do not match the actual land shapes, and surveyors may need to re-measure on site from scratch to reconcile them. Furthermore, when boundary markers are lost, restoration work relies on remaining markers or past survey drawings; small accumulated errors can leave uncertainty in boundary locations.

The same applies to as-built surveys: recording detailed ground shapes and the positions of structures requires measuring many points, which is demanding. Surveying can be difficult in steep terrain or heavily wooded areas, and adequate survey points may not be obtainable. Also, to convert survey results into drawings and reconcile them with the maps kept at the registration office (Article 14 maps) requires advanced accuracy control and data processing. Practitioners must carefully verify that measured point clouds and coordinates align with existing coordinate systems and control points, and may need additional surveys or corrections. These tasks consume time and effort and carry the risk of human error. To conduct boundary surveys quickly and accurately with limited personnel, efficiency gains through new technologies are indispensable.

Limitations of Conventional Surveying Methods (TS and GNSS) in Ensuring Accuracy

The traditional mainstays of boundary surveys—total stations (TS) and conventional GNSS survey instruments—each have strengths and limits. TS can perform distance and angle measurements with millimeter-level precision and is highly reliable for relative measurements over short distances. However, its operation requires manpower and time, which is a drawback. Heavy equipment must be transported and set up on site, and typically two or more people are required—one operator and another person holding a prism at each point. If there is uneven ground or obstacles, the instrument must be repositioned as necessary, and line-of-sight between survey points must be managed. Also, coordinates obtained with a TS must be tied to public coordinate systems via connections to known points or network surveys using multiple points; on its own it cannot be tied to absolute coordinates. Regular calibration and maintenance of the equipment are also essential, and handling it requires advanced expertise.

On the other hand, GNSS positioning, exemplified by GPS, uses satellites so it has fewer line-of-sight constraints and can obtain coordinates over wide areas. However, ordinary single-point GNSS positioning has large errors of about 5–10 meters and is unusable for boundary measurements. High-precision measurement requires techniques such as RTK (Real-Time Kinematic) or static surveying. Performing RTK with conventional GNSS devices involves preparing a base station (reference receiver) and a rover (mobile receiver) and transmitting correction information via radio or cellular networks—this also entailed a lot of hassle. If you set up your own base station, you must determine its position and configure communications; even when using wide-area network RTK services, you need network coverage and to bear monthly service fees. Furthermore, conventional GNSS equipment, including antenna and batteries, tended to be large and heavy, making transport nearly as burdensome as a total station. In forests or urban canyons satellite signals can be unstable, and it often takes a long time to obtain a fixed solution (cm-level precision). In short, conventional methods that balance accuracy and immediacy incurred high personnel and material costs.

How LRTK Achieves Centimeter-level Positioning and Its Stability

Against this backdrop, a new technology called LRTK has emerged. LRTK (Lightweight RTK) is a GNSS real-time positioning system that works with smartphones and can deliver centimeter-level positioning results on site instantly. Its mechanism applies real-time correction data to GNSS satellite signals for high accuracy. Specifically, it receives signals from multiple satellite systems (not just GPS but also GLONASS, Galileo, and Japan’s Michibiki (QZSS)) with a high-sensitivity compact antenna and cancels error sources such as satellite clock errors, ionospheric delay, and tropospheric delay using correction information. As a result, typical meter-level errors shrink dramatically to about 1–2 cm horizontally (about 3 cm vertically). Correction information can be delivered via cellular-network RTK reference station services, and LRTK also supports Japan’s quasi-zenith satellite Michibiki’s centimeter-level augmentation service (CLAS), allowing direct high-precision corrections from satellites even in mountainous areas without cellular coverage.

A key feature of LRTK systems is that high-precision positioning can be realized very easily. Using a compact dedicated GNSS receiver (roughly the size of a smartphone and weighing about 165 g), attached to a smartphone such as an iPhone and running an app, surveying can begin with a single operator. By mounting the smartphone on a pole with an antenna and using a bubble level to plumb it, point observations that previously required two people can be performed by one person with ease. During positioning, the app visualizes current accuracy and satellite tracking status, so you can see at a glance whether a fixed solution has been obtained. If errors are large, the app’s feature to automatically take multiple measurements and average them per point can improve accuracy. In practice, averaging 60 positionings at a point with LRTK produced horizontal accuracy of about 8 mm. With advanced positioning algorithms and the synergy of multi-GNSS, LRTK maintains stable centimeter-level accuracy 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 on maps and drawings. Combined with the lightweight compact equipment, it is an innovative solution that brings “precise positioning anytime, anywhere” to the field.

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

LRTK does more than measure point coordinates; it includes various functions that support fieldwork and deliverable creation end to end. A representative example is AR-based coordinate navigation. The app’s camera view can overlay pre-set target points or boundary lines, allowing invisible boundaries to be intuitively understood on site. For instance, if the coordinates of a boundary point to be restored are known, you can simply point the smartphone and approach the AR-displayed marker to locate the stake position within a few centimeters. Tasks that used to be performed by tracking angles and distances with surveying instruments—identifying “this is the boundary point”—can now be carried out visually and smoothly with AR guidance. When placing multiple points in sequence, the layout can be reproduced on site according to the map, so any misalignment with adjacent land or irregularities in straight lines can be noticed immediately. 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 matches the design).

Next is 3D point cloud recording. LRTK systems can use a smartphone’s LiDAR scanner, etc., to scan surrounding terrain and structures and obtain high-density point cloud data. These point clouds are georeferenced 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 and adjacent building positions around a boundary with a point cloud, you can later analyze positional deviations from the boundary in the office in detail, and you can measure elevation differences and structure heights. You can also calculate earthwork volumes for specific areas from point clouds or immediately perform analyses such as displaying differences from the design model as color-coded heat maps. 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 to georeference and align coordinates; this keeps overall errors low across large point clouds and enables accuracy control comparable to public surveying.

Cloud sharing is another important element of LRTK. Measured coordinate data, photos, and point clouds can be synchronized and saved to the cloud on site, eliminating cumbersome data organization after returning to the office. On the cloud, you can view each survey point’s position and attributes on a map, and by issuing a shareable URL you can immediately share results with stakeholders. For example, if a licensed land and house surveyor records a boundary meeting with positioning photos and uploads them to the cloud, colleagues waiting at the office can check and advise in real time. Because data are backed up automatically, survey results remain safe even if equipment is lost or damaged on site. It is also easy to retrieve past survey data via the cloud, so you can compare multiple surveys conducted over time to capture land changes. Compared with the era of exchanging paper maps or USB memory sticks, the ability to manage and share deliverables—including accuracy information—quickly and reliably is a major advantage well suited to modern surveying work.

Accuracy Verification Cases and Use Cases in Boundary Surveying

LRTK’s accuracy has been demonstrated through various verifications. One example reports positioning with LRTK at a known point assuming a first-class leveling benchmark (a national control point) and comparing the results with coordinates obtained by another high-precision GNSS instrument. The differences in both horizontal and vertical directions were below a few millimeters, confirming that LRTK’s accuracy is comparable to that of expensive conventional survey instruments. In another case where about ten boundary markers were measured consecutively, the relative errors between points were within 1 cm, and averaging multiple measurements reduced the maximum error to around 5 mm. These accuracy verifications suggest that LRTK can sufficiently meet the standard required for Article 14 maps—namely, that boundaries can be restored on site within a specified error range.

There are many practical use cases. For measuring boundary points, LRTK can quickly obtain the coordinates of each parcel corner. Whereas conventional workflows used TS for traverse calculations, LRTK provides plane rectangular coordinates directly on site, enabling immediate drafting. Measured points can be supplied to the registration office as coordinates for Article 14 maps, reducing later coordinate conversion and adjustment work. While surveying, you can check the straightness or bend angles of boundary lines on the app, allowing you to verify whether each point is ideally placed as you proceed. If existing boundary markers disagree with old public maps, you can instantly quantify the discrepancy, which makes it easier to explain to stakeholders during on-site meetings.

LRTK also gives confidence in boundary marker restoration and installation. When restoring a lost marker, if the pre-calculated coordinates are input into the app, AR navigation will guide you to the installation position on site. There is no need to rely on experience and intuition with tapes or measuring staffs to estimate positions, enabling quick and accurate installation. After installation, you can immediately re-measure the point with LRTK to verify that the coordinates match the planned values with a single tap. This lets you preserve evidence that the restored marker lies within the prescribed error range. If a dispute arises later, you can present the positioning data and photos stored in the cloud as objective proof.

LRTK is also effective in as-built surveys and drawing reconciliation. For cases such as residential land development or parcel subdivisions, it is necessary to accurately capture not only boundary lines but also the positions of existing structures (fences and buildings) and terrain undulations. By measuring boundary points with LRTK while simultaneously scanning the ground surface into a point cloud, you obtain comprehensive “as-built restoration” data for the site. From the acquired point cloud you can create an as-built plan of the entire lot and overlay design drawings or registered boundaries to immediately see discrepancies between design and reality. If a fence encroaches, you can precisely compute the distance, and conversely, if the distance from the boundary to a building is extremely large, you may consider whether land use is inefficient. In this way, LRTK’s positioning and point cloud technologies support multifaceted as-built understanding centered on boundary lines.

There are also administrative and public-survey use cases, such as emergency surveying immediately after disasters. Even in areas where many boundary markers were displaced or washed away by earthquakes or landslides, if Article 14 maps are in place the coordinates of lost boundaries remain. LRTK can position even when only power is available and communications infrastructure has failed, so it is being adopted for rapid boundary restoration and terrain surveying in disaster areas. For example, LRTK was used following the Noto Peninsula earthquake to record and share damage along evacuation routes using positional photos. The mobility that enables reliable spatial information to be recorded in situations that were previously difficult is proving valuable beyond the scope of routine boundary surveying.

Benefits of Adoption: Reduced Workload and Increased Reliability of Deliverables

From the technical features and practical examples described above, many benefits of adopting LRTK become apparent. First is a significant reduction in workload. Surveys that used to require two skilled personnel can be completed by one person, leading to reduced labor costs and greater scheduling flexibility. The physical burden of carrying heavy equipment over long distances disappears, reducing on-site physical stress. Time spent on site setup and cleanup is shortened, increasing the volume of work that can be completed in a day. Especially for wide-area parcel identification tasks and surveys with many points, dramatic efficiency improvements over conventional methods can be expected.

Improvements in drawing consistency are also noteworthy. Coordinates obtained with LRTK are natively in public coordinate systems, so errors or mistakes that occur during conversion to other coordinate systems in post-processing are avoided. Combining results from adjacent survey sites is less likely to produce mismatches, resolving problems where stitched drawings did not align. This makes it easier to secure a high accuracy classification for maps filed with the Legal Affairs Bureau. When land area is calculated from boundary point coordinates, increased confidence in that accuracy can also facilitate smoother consensus-building among stakeholders.

Regarding increased reliability of deliverables, digital data brings objectivity and reproducibility. Points measured with LRTK are recorded in the cloud along with timestamps and accuracy information, leaving no room for arbitrary tampering or subjective interpretation. Sharing on-site measurements during boundary meetings helps landowners feel reassured. If doubts arise later about whether the correct location was measured, recorded data can be validated by third parties. In this way, transparent surveying contributes to improving trust in matters related to land boundaries. Height information, which is difficult to convey with paper maps, can be supplemented with 3D point clouds to present terrain and boundary conditions three-dimensionally, greatly enhancing explanatory power. This is useful in registration procedures and mediations of boundary disputes, where deliverables backed by accurate data provide reassurance to all parties.

Conclusion: Everyday Use and the Potential Opened by LRTK

To address the challenges of ensuring accuracy and improving efficiency in the creation and maintenance of Article 14 maps, LRTK offers a groundbreaking solution. By combining the stability of centimeter-level GNSS positioning with advanced features such as AR, point clouds, and cloud services, LRTK enables consistent accuracy control from field surveying through deliverable creation. The benefits are not limited to official surveying work carried out by licensed land and house surveyors or surveyors: the ease and immediacy of LRTK mean it also has potential for routine, simple surveys and regular on-site records.

For example, LRTK’s high accuracy can be applied to quick checks of adjacent boundaries between survey tasks or to fixed-point monitoring of ground settlement before and after construction—small daily measurements that used to be omitted can now be recorded accurately, reducing later regrets about missed measurements. Because cloud-based data management makes it easy to accumulate survey data, new initiatives such as using collected data in a GIS for land management are also possible. With precision positioning that was once expensive and difficult now accessible to anyone, the style of surveying itself is changing.

LRTK, which dramatically improves the reliability and efficiency of boundary surveying, makes a tangible contribution to raising the accuracy of Article 14 maps while broadening the scope of surveying work. As mobile high-precision positioning technology becomes more widespread, more parcels will have accurately determined boundaries, facilitating smoother registration procedures and land use. By adopting LRTK—which combines accuracy and convenience—boundary surveying can be freed from previous constraints and new possibilities can be opened. For greater on-site assurance and improved reliability, consider proactively incorporating such advanced tools.