What is the Nationwide Road Base Map and Related Databases? Five Basics to Know Before Viewing

Table of Contents

• Understand the role of the nationwide road base map and related databases

• Basics 1: Understand the difference between road base map information and road register appendices

• Basics 2: Understand that the information viewable is not the actual current on-site conditions

• Basics 3: Organize beforehand the points to check in practical work

• Basics 4: Check the drawing's scale, position, and update timing

• Basics 5: Make judgments by combining on-site verification and survey data

• Approach to leveraging the nationwide road base map and related databases in practice

• Summary

Understanding the Role of the National Road Base Map and Related Databases

The National Road Base Map Database is a database that makes road base map information and road ledger attached maps related to directly managed national highways, etc., easy to view centrally on the web. In publications by the Ministry of Land, Infrastructure, Transport and Tourism, it is described as an environment that enables centralized use of the detailed plan view map data that had been accumulated and managed by each road administrator. Public access began on May 31, 2024, and the system has been developed to allow viewing of road base map information and road ledger attached maps for directly managed national highways, etc., on a map.

Practical situations in which staff consult this database include road boundaries, road structures, attachment maps of the road register, construction plans, maintenance management, occupancy consultations, field surveys, and preliminary investigations before design. In particular, for road-related work, the ability to grasp early clues about the positional relationships of the target location and the extent of management affects the accuracy of subsequent surveys and the amount of rework required. If the amount of information that can be checked at a desk before visiting the site increases, it becomes easier to organize which locations to inspect during the field survey, which documents to bring, and which items to confirm with stakeholders.

However, the National Road Base Map and related database are not a universal resource that allows all judgments to be completed as soon as you open them. Road base map information and road ledger supplementary maps are affected by the time of creation, the scope of coverage, conversion methods, the display environment, update timing, and so on. Therefore, before viewing them it is important to understand "what the data is intended to show," "what can be appropriately determined from it," and "from what point onward you need to check the original documents or conduct on-site verification."

This article explains five fundamentals that practitioners accessing the National Road Base Map Database and related datasets for the first time should grasp before viewing it. Rather than merely a how-to guide, it organizes the points that are easily misunderstood in practice, the recommended order of checks, and how to connect the data to fieldwork.

Fundamentals 1: Grasp the differences between Road Base Map Information and Road Ledger Attached Maps

The first thing to grasp when understanding the National Road Base Map Database and related datasets is that Road Base Map Information and Road Ledger Attached Maps are not the same. Both are treated as planar map data concerning roads, but their nature and purposes for creation differ. If you view them without understanding this difference, you may interpret the lines and areas displayed on the screen as having the same meaning, which can lead to discrepancies in judgment in later stages.

Road base map information is two-dimensional GIS data that depict road structures based on the shape of the road at the time of completion of road construction. The data are organized into layers for multiple features, such as carriageways and distance markers. It is characterized by being easy to understand road structures on a map and easy to use for considerations such as design, maintenance management, surveys, and system integration.

On the other hand, the supplementary map of the road register corresponds to the drawings of the road register whose preparation and custody are prescribed by Article 28 of the Road Act. It is treated as basic reference material for confirming the road’s area, width, route, structures, and matters necessary for road management. The supplementary map of the road register is primarily an administrative management document and is important for confirming road areas and management scope. However, it should be noted that the information shown does not, in itself, indicate land boundaries or rights relationships.

In practice, it is easier to understand if you regard Road Base Map Information as "map data for understanding road structure" and Road Ledger Attached Maps as "drawing materials for road management." For example, Road Base Map Information is useful when you want an overview of the roadway, sidewalks, road geometry near intersections, or the locations of distance markers. On the other hand, when you want to verify the road area or the entries on ledger drawings, you need to place greater emphasis on Road Ledger Attached Maps.

What’s important here is that it isn’t always sufficient to look at just one source. The information you need to consult changes depending on whether you want to grasp the road structure, verify the information in the official records, or perform preliminary checks before an on-site survey. Even when multiple pieces of information can be overlaid and viewed on the screen, distinguishing each item’s creation background and meaning when you read them is the first step to preventing practical misunderstandings.

Fundamentals 2 Understand that the information you can view is not the actual current condition

When viewing the National Road Base Map and related databases, the most important thing to be careful of is not to assume that the information displayed represents the current conditions. Roads are public infrastructure used daily, and their condition can change due to construction, repairs, disaster recovery, changes in occupancies, roadside development, intersection improvements, and other factors. Drawings and map data are compiled based on information available at the time they were created, so they may not match the actual on-site conditions at the time of viewing.

With regard to road base map information, for national highways it is based on drawings delivered as deliverables from road construction and other works from fiscal 2006 onward, and sections where no road construction took place may not be displayed. Road base map information for expressways has also been compiled based on as‑built drawings of road works submitted from fiscal 2006 onward. In other words, whether something is displayed and its content are influenced by past construction results and submission/delivery status.

Regarding the supplementary maps attached to the road register, the recorded information reflects the state at the time of preparation, and due to the timing of updates and related factors the shape of the road and other details may differ from current conditions. It is also noted as a caution that the shapes of structures outside the road area, facility names, lot numbers, locations, and similar details may not be accurate. Materials that have been converted from documents previously kept on paper may also result in sections that do not display or sections where the display is distorted.

Therefore, when using it in practice, it is safer to consider the National Road Base Map database and similar databases not as materials for omitting on-site verification but as preliminary materials to improve the accuracy of on-site verification. By reviewing them, you can grasp roughly where road areas are, which segments have drawings, and which facilities or configurations warrant attention; thereafter, it is desirable to make judgments by cross-checking with on-site photographs, survey results, confirmation from the managing authority, existing drawings, and design documents.

In particular, caution is required when using them for construction planning or consultation documents. If you determine the construction extent, road areas, boundaries with private land, occupancy locations, clearances from structures, etc., solely on the basis of the positions of lines seen on a screen, you may later discover inconsistencies with original documents or field surveys. At the viewing stage, it is important to treat such findings as hypotheses and to always corroborate any important decisions by overlaying verification materials.

Basics 3: Organize in Advance the Key Points to Check in Practice

The National Road Base Map and related databases are a convenient entry point for checking detailed road-related information, but if you open the interface without a clear purpose, it can be hard to know where to look. Before browsing, it is important to organize the items you want to confirm for the specific task. The aspects to check differ for road management, design, construction, inspection, surveying, consultation, and document preparation.

For example, when confirming matters related to road management, it is important to determine which route or section the subject location falls under, the positional relationship of distance markers, whether an attached map of the road ledger exists, and whether there are materials available that can be used to verify the road area. If the confirmation is prior to design or construction, the focus is on understanding the shape of the roadway and sidewalks, the tie‑ins at intersections, the positional relationship with structures, and the points that require attention during on‑site surveys.

In preliminary checks concerning occupation and adjacent work, it is important to identify whether locations are inside or outside the road area, the relationship with existing facilities, and any points that are likely to require confirmation with the road administrator. However, because the boundary lines of road areas shown on the map attached to the road ledger do not represent land boundaries or rights relationships, separate confirmation is required when making determinations about land boundaries or ownership. Misunderstanding this point could cause the assumptions of consultation materials and construction plans to become misaligned.

When reviewing materials in preparation for a site survey, it is effective to identify the directions to photograph on site, the points to survey, the structures to verify, and the locations that require caution for traffic and safety management. By reviewing road base map information and the road ledger supplementary maps in advance, it becomes clear which documents to cross-check after arriving on site. In particular, roads involve many overlapping elements—intersections, bridges, retaining walls, slopes, sidewalk edges, drainage facilities, signs, lighting, and lane markings—so trying to confirm everything from scratch on site makes omissions likely.

Also, when reviewing, it is important to look not only at the specific location but also at the adjacent sections before and after. Road structures are not completed at a single point; they have continuity in both the longitudinal and transverse directions. By checking a little before and a little after the target location, you are more likely to notice changes in road width, intersection geometry, transitions between structures, and changes in management sections. In practice, this before-and-after check is effective in preventing rework.

Fundamentals 4: Confirm the drawings' scale, position, and update timing

When using the National Road Base Map and related databases in practice, you need to pay attention to the scale, position, and timing of updates of the displayed drawings and data. When layers are overlaid on the map, everything may appear to be of the same accuracy, but in reality how they are interpreted varies depending on the time of creation, original sources, conversion methods, and the display environment.

Maps attached to the road ledger should be used with attention to their original paper size and scale. Just because they can be zoomed in or out on the screen does not mean they will always be displayed or printed at the correct scale. Depending on the viewing environment or print settings, the apparent size may not match the actual scale. When handling dimensions or positions precisely, do not rely solely on the on-screen appearance; verify them against the original documents, official drawings, and field survey results.

The same applies to location. The drawing-section information in the road ledger appendix map is considered to be information such as route numbers, branch numbers for new/old roads, and start/end distance markers converted into latitude and longitude and displayed on the map, and due to deficiencies or omissions in the drawing-section information or the data used for conversion, it may not be displayed in the correct position. This is a very important point to note when verifying displayed positions on the map.

It is also essential to check the update timing. The entries in the road ledger attached maps reflect the time they were prepared, and the shape of the road may have changed since then. In sections where road improvements, widening, intersection modifications, sidewalk works, bridge repairs, pavement maintenance, slope countermeasures, disaster recovery, and the like have been carried out, you need to confirm on the assumption that current conditions may not match the drawings. If you proceed with preparing materials without considering that the information you viewed may be outdated, revisions may be required at the stage of field verification or consultation with the managing authority.

In practice, when you look at drawings you should not immediately reach a conclusion; first confirm "what point in time or state does this information represent?", "how reliable is this displayed position?", and "is it appropriate to judge dimensions based on the scale?". Information obtained on a viewing screen is useful as an entry point for consideration, but if you are going to treat it as material to determine dimensions, boundaries, construction locations, occupancy positions, or the scope of management, you must verify it against official documents and on-site measurements.

Fundamental 5 Make judgments by combining on-site inspections and survey data

The value of the national road base map and related databases increases when they are combined with on-site verification and survey data, rather than when used to draw conclusions on their own. In road-related practice, it is important to cross-check information verified in the office with information obtained in the field to identify discrepancies. The databases are effective for that preliminary organization and play a role in improving the quality of fieldwork.

During on-site verification, the road geometry, distance markers, intersections, structures, road edges, sidewalks, slopes, drainage facilities, etc., that were checked in the Road Base Map Information and the road ledger appendix maps are compared with the actual conditions. Locations where the on-screen information matches the field conditions become easier to use as the basis for subsequent work. Conversely, at locations with discrepancies, it is necessary to check the timing of drawing updates, on-site alterations, display misalignment, misreading, and insufficiency of management documents.

Combining survey data is also important. By cross-referencing coordinates, elevations, photographs, point clouds, and measurement notes obtained in the field with the road information reviewed beforehand, you can improve the reliability of the documentation. Especially for pre-construction surveys, as-built verification, and design studies near roads, field measurements—not just map information—are important. Even if lines appear to align on the screen, they may be offset from the actual positions of curbs, pavement edges, structures, boundary markers, and roadside appurtenances.

Also, national road base map and related databases are useful when organizing information collected in the field afterwards. They make it easier to clarify which route and which section a photo was taken on, near which distance marker a survey point was recorded, and which drawings should be cross-checked. If photos taken in the field and survey notes are not linked to location information, it takes time to verify them later. By identifying the target sections in advance and deciding on a method for managing field data, you can reduce the effort required to organize the materials.

What's important during on-site inspections is to record differences on the spot when you find them. For locations where the drawings appear to differ from the actual conditions, leaving photos, the location, orientation, nearby landmarks, the survey point number, the inspector, and the date and time of inspection will make it easier to explain to managers and stakeholders later. In road-related practice, records that show the location and current conditions are more effective than explanations based on memory.

Approach to Applying the National Road Base Map and Related Databases in Practice

To put the National Road Base Map and related databases to practical use, it is important to be mindful of the flow of viewing, confirming, recording, cross-checking, and sharing. Rather than simply opening the screen and looking at the target location, deciding in advance what to confirm, what information to supplement on site, and which documents to update will affect the efficiency of your work.

Before you begin viewing, first clarify the target route, the specific section, and the purpose of the review. Depending on whether you want to confirm the road area, understand the road structure, organize the assumptions for a construction plan, or identify checkpoints for a field survey, the information you need to look at will differ. If you review the data with an unclear purpose, you will only end up looking at the information on the screen and it will be difficult to arrive at the necessary decisions.

Next, record any uncertainties observed during viewing. Sections that do not display, areas where drawings are distorted, locations that may differ from current conditions, places where road limits and land boundaries are easily confused, and spots requiring attention due to scale or printing should be left as items to be confirmed in later stages. The National Road Base Map and other databases are convenient, but as noted in the usage precautions, you cannot necessarily make important decisions based solely on the displayed content. Important decisions should be made by combining official documents and on-site verification.

On-site work involves assembling the order of checks based on information reviewed beforehand. Rather than inspecting only the target locations, we check the sections before and after, intersections, areas near administrative boundaries, areas near structures, road edges, sidewalk edges, drainage facilities, and the surroundings of signs and related fixtures. This is because information about roads often has meaning not as isolated points but in relation to their surroundings. Photos and survey results obtained on site are organized by linking them with location information and survey point names so they can be cross-checked with drawings later.

When preparing documentation, it is important to organize separately the information confirmed from databases and the information obtained from on-site verification. If you mix what was identified through desk review, what was confirmed on-site, and what remains unconfirmed, it becomes difficult to explain during discussions with stakeholders. Especially in projects involving road authorities, contractors, designers, clients, and partner companies, clarifying the source of information and the status of its verification helps reduce misunderstandings.

Furthermore, to streamline on-site data collection, using smartphones for location-tagged records and survey data management is also effective. If, based on the target sections checked in advance in databases such as the National Road Base Map, you can record photos, notes, coordinates, point clouds, and so on on site, cross-referencing work after returning to the office becomes easier. Paper notes and photos alone can make it time-consuming to pinpoint locations later, but if on-site data are linked to location information, it becomes easier to verify them against road drawings.

Summary

The National Road Base Map Database is a useful resource for road professionals that enables centralized viewing of road base map information and road ledger annex maps for directly managed national highways and other roads. Being able to review detailed plan information of roads in advance helps with preparations for road management, design, construction, inspection, field surveys, and the preparation of consultation materials.

However, the information available for viewing is not necessarily the same as the current conditions. Road base map information is data based on construction deliverables, and the road ledger's attached maps are drawings that show the contents as of the time of their preparation. There may be sections that are not displayed, display irregularities, differences in update timing, misreading of scale, positional shifts, and other issues. Therefore, do not finalize important decisions based solely on on-screen information; it is important to make judgments by combining original documents, confirmation with the managing authority, on-site verification, and survey data.

The basics to grasp before viewing are: understanding the difference between Road Base Map Information and the Road Ledger Attached Map, viewing it on the assumption that it may differ from current conditions, organizing the items you want to verify in practice, paying attention to scale, position, and update timing, and combining it with on-site verification and survey data. If you keep these five points in mind, the nationwide Road Base Map and related database will be easier to use not just as a mere viewing screen but as a verification foundation to reduce rework in practical operations.

At road-related sites, it is important to verify information seen at the desk on site and to record it as photographs, location information, and survey results. After identifying the target section using the national road base map and other databases, the accuracy of the data collected on site and the method used to organize it determine the quality of the work. If you want to efficiently keep on-site checks and survey records and advance reconciliation with road drawings and map information, using LRTK Phone, a smartphone-based surveying solution, is also one option to consider.