Six steps to look up road information in the National Road Base Map and related databases

The National Road Base Map Database is a publicly accessible database for viewing detailed plan-view map data related to roads—such as road base map information and maps attached to road ledgers—for directly managed national highways and similar roads. In practical work that handles road information—road management, pre-design surveys, occupancy consultations, maintenance, ledger verification, preparation for field surveys, and so on—there are often situations where practitioners are unsure which documents to consult first, how far they can rely on them, and how they should be combined with on-site verification. This article explains, for practitioners who use the National Road Base Map Database to investigate road information, a six-step workflow for verification. It organizes the verification procedure to be useful in practice, covering not only on-screen operations but also cross-checking maps attached to road ledgers, road base map information, drawing sections, existing documents, and actual site conditions.

Table of Contents

• Understand the information available in the National Road Base Map and related databases

• Step 1: Clarify the intended use and organize the road information to be investigated

• Step 2: Identify the target location on the map and check surrounding conditions

• Step 3: Display the road register attachment maps and the mapped section to confirm the location of materials

• Step 4: Switch layers of the road base map information and interpret the road structure

• Step 5: Cross-check with existing documents and on-site conditions to gather decision-making materials

• Step 6: Record survey results and use them to inform updates and on-site surveying

• Summary: Verification of road information combines database checks with on-site measurements

Understanding the information available in the National Road Base Map and related databases

Before checking road information in the National Road Base Map and Related Database, it is important to first understand what this database is intended to verify. Even when speaking generally of road information, the data handled in practice is wide-ranging: road location, road structure, the shapes of carriageways and sidewalks, distance markers, drawings related to road areas, appendices to road ledgers, as‑built drawing information from construction completion, and materials held by managing authorities. The National Road Base Map and Related Database is a system designed to make it easier to view these kinds of planimetric road map data centrally.

The first point practitioners should grasp is that the information visible on the screen does not necessarily constitute the entirety of the final decision. Road base map information is treated as map data that represents road structures based on deliverables from road construction and on as-built drawings of road construction. Road ledger supplementary maps are referenced as drawings related to the road ledger under the Road Act. Both are useful for verifying road information, but the scope of their applicability and the points that need to be checked vary depending on the time of creation, the scope of works covered, the update status, and their relationship with management documents.

For example, if you want to grasp the approximate location and shape of a road, simply displaying the target road on a map can provide a lot of information. On the other hand, for decisions near boundaries, confirmation of the positions of occupying objects, determination of construction extents, register updating, quantity calculation, and preparation of materials for explaining to stakeholders, you should not rely on on‑screen display alone; it is necessary to cross-check with the road register, existing drawings, site photographs, survey results, and materials held by the manager.

The purpose of using the National Road Base Map and related databases is not simply to view road information. It is to identify where documents related to the target road are located, narrow down the necessary information, and clarify which documents should be checked next and the key points for on-site surveys. Therefore, rather than pursuing detailed numerical values from the outset, it is important to sequentially organize the overall picture of the target section, the types of information displayed, the scope of the documents, and the locations that require on-site verification.

In particular, in road management operations, problems frequently occur, such as old drawings not matching current conditions, uncertainty about whether post-construction updates have been applied, discrepancies between paper records and electronic data, and multiple departments referring to different documents. The National Road Infrastructure Map and related databases are useful as a starting point for such verification work, but for final practical decisions it is essential to ensure that the supporting documents align with the actual conditions on site.

Step 1 Organize the intended use and the road information you want to investigate

Before opening the National Road Base Map and related databases, first clarify your intended use. If you start viewing the map while this is still vague, the large amount of displayable information makes it difficult to know which layers to check and which sources to use as a basis. In practice, the items you need to examine vary greatly depending on the purpose for which you are researching road information.

For example, whether you want to check for the presence of a road ledger annex map, understand the shape of the roadway and sidewalks from road base map information, examine the positional relationships of distance markers and road structures, or confirm the surroundings of a planned construction section will change both the order of operations and what should be recorded. For preliminary checks for occupancy consultations, the positional relationships between the road area and existing facilities become important. For maintenance or repair planning, the items to confirm include paving extents, intersections, sidewalks, and the shapes around structures. For updates to the road ledger, you need to check whether there are any differences between the existing ledger annex map and the current road shape.

At this stage, what’s important is to verbalize as specifically as possible the information you want to investigate. Saying “check road information” is too broad. If you break the objective down into work-sized tasks such as “confirm which sections of the target route have road ledger appendix maps,” “understand the sidewalk layout around intersections,” “compare the planned construction area with existing road base map information,” and “identify locations that require on-site surveying,” it becomes easier to avoid overlooking anything.

Also decide how the deliverables will be used along with the intended purpose. Whether it is a reference document for internal review, a pre-design study document, an instruction sheet for on-site surveys, or an explanatory document for consultations will affect the required level of accuracy and the amount of supplementary materials. For informal checks, understanding via on-screen review may be sufficient, but when the matter relates to formal decisions or external submissions, it is necessary to clarify the source materials, the creation date, and the results of on-site verification.

Road information is not confined to the lines and polygons visible on a map. Roads change condition due to daily maintenance, improvement works, works that occupy the road, disaster recovery, and roadside development. Therefore, when using national road base maps and related databases, it is important to be aware of what point in time the information reflects, whether there may be discrepancies with conditions on the ground, and what points should be confirmed with other sources.

As an initial step, briefly note the route name, the section to be checked, the intended use, the types of information to be verified, the purpose of the deliverables, and whether an on-site inspection is required; doing so will stabilize subsequent work. In particular, when multiple people are conducting the survey, without this organization misunderstandings easily arise—for example, one person may be looking at the ledger attachment map while another is only consulting the road base map information. When checking road information, clarifying the objectives before carrying out screen operations has a greater impact on quality than the screen operations themselves.

Step 2: Identify the target location on the map and confirm surrounding conditions

After clarifying the intended use, next identify the target location on the map. In databases such as the National Road Base Map, use the map view to check the road in question and its surrounding area. The important thing here is not to display detailed plan information right away, but to first grasp the location of the target road over a wide area and then zoom in to the required scale.

When searching for a target location, combine the information you have—place names, latitude and longitude, route numbers, distance markers, intersection names, nearby facilities, structures such as bridges and tunnels, and locality names included in construction project titles—to narrow down the position. In road registers, design drawings, and construction documents, sections are sometimes indicated by route names, distance markers, or start/end point expressions rather than by addresses. On the other hand, field survey personnel may identify locations by addresses or facility names. It is important to reconcile these different ways of expressing locations and confirm that they refer to the same point on the map.

Once you can display the target location, check the surrounding conditions. When reading road information, not only the subject road itself but also surrounding conditions such as intersecting roads, side roads, sidewalks, rivers, railways, public facilities, points of contact with private land, bridge sections, tunnel sections, slopes, retaining walls, and entrances and exits are important. Even when looking at maps attached to the road ledger or road base map information, in places where these conditions exist the representations on the drawings tend to become complicated, and on-site verification may be necessary.

Especially near intersections and around structures, road boundaries, sidewalk shapes, roadway edges, gutters, planting strips, and driveway entrances may be displayed close together, so viewing a road as a simple line can easily lead to misunderstandings. When using this for maintenance or construction planning, it is practically useful to check not only the sections immediately before and after the target segment but also the connecting roads and the area that may be affected.

Also, even after identifying the target location, information may not appear on the map. There are several possible reasons for this: the road may be outside the target scope, the data may be unprepared, the layer to be displayed may not be selected, the scale may be inappropriate, or the information may be managed in different materials. Rather than concluding that road information does not exist just because it is not displayed, you should check the display settings, the target scope, the managing authority, and how it is labeled in your on-hand materials.

Identifying the target location on a map provides the foundation for subsequent verification work. Even a slight positional shift can cause you to look at a different registry annex map or to rely on road base map information from an adjacent section. Therefore, it is important to confirm the target location using multiple clues — not just the on-screen appearance — such as the route name, the lot frontage, nearby intersections, and approximate distances.

Step 3: Display the road ledger appendix map and the mapping section to confirm the location of the materials

Once the target location has been identified, confirm the road ledger annexed map and the drawing section. The road ledger annexed map is a drawing related to the road ledger whose preparation and storage are stipulated by Article 28 of the Road Act, and it holds an important position in the practical management of roads. In the National Road Base Map and related databases, you can view information related to the road ledger annexed maps on the map to help identify the applicable drawings and drawing sections.

The first things to check in this procedure are whether the attached map in the road ledger is displayed for the target section and what range is indicated as the drawing section. By confirming the drawing section, it becomes easier to understand which drawing(s) may include the target location and how it connects to the adjacent sections. In some cases, checking the drawing section first, rather than searching directly for the attached map in the road ledger, makes it easier to organize where the materials are located.

When viewing maps attached to the road register, pay attention not only to the map’s displayed coverage but also to the purpose for which the map was created and its update status. Maps attached to the road register are important materials for road management, but their displayed content reflects the situation at the time of preparation and does not always match the latest on-site conditions. If road improvements, sidewalk construction, intersection upgrades, works that occupy the roadway, disaster recovery, area changes, or similar projects have been carried out, differences may arise between the register maps and the actual site. Therefore, while treating the maps attached to the road register as important reference materials, make judgments in combination with other documents and on-site verification as necessary.

A common mistake in practice is to assume that verification is complete simply because the map attached to the road ledger could be displayed. In reality, you need to determine which extent of the drawing was viewed, where the target point is located within the drawing, whether it falls on the edge or at a connection of the drawing, and whether adjacent drawings should also be checked. Especially at section boundaries and near intersections, a single sheet may not be sufficient to fully grasp the surrounding relationships.

When checking the supplementary map of the road ledger, carefully examine how lines related to the road area and road structure are represented. Points of focus vary depending on the purpose of the work, such as width, centerline, side ditches, sidewalks, slopes, structures, and depictions near boundaries. However, the supplementary map of the road ledger does not certify the contents displayed, and the boundary lines of the road area do not indicate land boundaries or rights relationships. When details of dimensions, boundaries, rights relationships, or formal determinations are involved, it is necessary to verify the original materials, surveying results, and with the road administrator.

At this stage, recording the names and coverage of the attached maps in the road register, the map sections that could be displayed, their relationship to the target locations, any information that could be useful for decision-making, and points that require additional verification will make it easier to review the work later. Because checking road information often cannot be completed in a single pass, keeping a record of which documents you consulted helps prevent rework.

Step 4 Toggle the Road Base Map Information layers to read road structure

After confirming the attached maps of the road ledger and the mapping section, next check the layers of the Road Base Map Information. The Road Base Map Information represents road structures as two-dimensional GIS data based on the form of the road at the time road construction was completed. Because features related to road structure—such as roadways, sidewalks, and distance markers—are organized by layer, you can review the required information by switching layers as needed.

When checking layers, it is important not to display everything from the start but to show them incrementally according to the purpose. Displaying a lot of information at once causes lines and surfaces to overlap and become hard to read, which can lead to misinterpretation. First grasp the overall shape of the road in question, then sequentially check the necessary items—such as the carriageway, sidewalks, distance markers, and information related to road appurtenances and structures—so that it is easier to understand the road’s composition.

When reading road base map information, it is important not to view the road merely as a centerline but to be aware of the road space as an area. In road management and construction planning, not only the position of the carriageway but also the spatial configuration of sidewalks, shoulders, medians, intersection areas, vehicle access points, and areas around structures are important. Especially during field surveys and pre-design checks, it is necessary to combine multiple layers to determine where a feature is located within the road space.

The positions of distance markers and the positional relationships between sections are also important items to verify in practice. In road construction and maintenance documents, locations are sometimes indicated not only by address but also by distance markers and start/end points. If distance markers and road alignment can be confirmed on a map, it becomes easier to explain the survey location on site and reduces misunderstandings among stakeholders. However, when using the positions of distance markers or road alignment to determine precise construction extents or quantities, verification through field surveying and comparison with management records is required.

When switching layers to review, be careful not to judge the existence of a road or facility solely by whether information is displayed. Road base map information is based on drawings and other deliverables submitted as results of road construction and similar works, so sections where no road construction has taken place or where development is incomplete may not be displayed. Also, in sections where road construction has not been carried out, where data have not been digitized, or where pre-update information remains, there may be discrepancies with conditions on the ground. If information is not displayed, do not determine the reason by guesswork; it is necessary to supplement it with other sources or on-site verification.

The results of checking road base map information become more practically valuable when viewed together with the attached maps in the road ledger. Confirm the extent of the materials and their management classification on the ledger’s attached maps, and read the road structure layer by layer from the road base map information to deepen your understanding of the section in question. Rather than relying on just one source, combining multiple pieces of information is the basic principle of road information surveys.

Step 5 Assemble decision-making materials by cross-checking existing documents and on-site conditions

After checking the road ledger attached maps and road base map information in the National Road Base Map database, next cross-check them with existing documents and the actual site conditions. This is one of the most important procedures in practice. Information that can be confirmed on maps is useful, but road information is established in relation to the actual site conditions, past construction work, management records, survey results, occupancy information, update history, and so on. If you rush to a conclusion based only on on-screen information, discrepancies may be discovered later.

Materials to be cross-checked may include the road register, past road register annex maps, as-built drawings, design drawings, survey maps, occupancy-related documents, maintenance history, site photographs, inspection records, and materials from consultations with relevant agencies. The documents required vary depending on the purpose of the task, but what is commonly important is to clearly specify which documents will serve as the primary reference materials and which will be treated as supplementary.

For example, when investigating to update the road register, the differences between the existing register's attached maps and the current conditions are important. For a pre-design survey, it is important to confirm the current road geometry, structures, roadside conditions, occupancies, drainage facilities, and so on. For occupancy consultations, it is necessary to confirm how the location of the object in question relates to the road area and existing facilities. For maintenance management, it is necessary to organize the location of repair targets, surrounding structures, impacts on traffic, management classifications, and so on.

When matching on-site conditions, it is effective to organize the information seen on the map in a form that can be taken directly to the field. If you compile in advance the start and end points of the target section, locations you want to check, places where drawings and the site may differ, directions in which to take photos, points requiring surveying, and items to confirm with stakeholders, the efficiency of the field survey will improve. On site, check not only the road alignment but also elements that are easy to overlook on drawings, such as pavement edges, drainage gutters, curbs, sidewalks, slopes, structures, signs, lighting, encroachments, manholes, entrances and exits, and areas near property boundaries with private land.

When cross-checking, what you should pay particular attention to is the road's update history. After road improvements or repairs are carried out, not all sources are necessarily updated at the same time. One source may reflect the new configuration while another may still show the old configuration. If the information confirmed in the National Road Base Map and other databases differs from the drawings you have on hand, rather than immediately judging one of them to be wrong, check the creation date, update date, purpose of creation, managing department, and scope of coverage.

Also, when using road information in external briefings or consultations, it is important to keep a record of the verification results. Recording which data were consulted, which existing materials they were compared with, what was confirmed on site, and where discrepancies were found makes it easier to explain the rationale behind decisions later. When verifying road information, you are expected not only to locate the correct information but also to be able to explain the decision-making process.

Step 6 Record survey results and link them to updates and on-site surveying

After researching road information, record the verification results and carry them forward to the next tasks. Investigations using the National Road Base Map and other databases do not end with just looking at the screen. Only by recording what was confirmed, organizing items that require additional verification, and, as necessary, proceeding to field surveys, ledger updates, preparation of design documents, and preparation of consultation materials, does the work become a practical, actionable outcome.

Items to record include the subject route, the relevant section, the date of inspection, the types of information checked, the displayed road ledger attached map, the mapped section that was checked, the layers of the road base map information that were referenced, differences from existing materials, the need for on-site verification, and any uncertain points that cannot be used for decision-making. By keeping these records, you can reduce duplicated work when rechecking the same location later.

What's particularly important is to record separately what was determined and what was not. When checking road information, it's easy to focus only on the displayed data, but in practice the information that could not be confirmed can be the most important. Points such as drawings not being displayed for the target section, only part of the road base map information being viewable, existing documents not matching the on-site conditions, difficulty in judging areas near boundaries, and difficulty in reading the shapes around structures are all information that must be handled in subsequent work.

The recorded results can also be used for planning on-site surveys. Based on the target sections identified on the map, organize the locations to be photographed on site, the points to be surveyed, the structures to be checked, and the items to be confirmed with relevant parties. Narrowing down the scope of on-site verification in advance can shorten work time and reduce survey omissions. Accurately understanding the differences between drawings and the field is especially important for updating road registers and for maintenance management.

When using data to update road information, you need to consider how to organize the information collected on site. Photographs alone can make it difficult to understand positional relationships, and paper notes can be hard to share later. If you manage location information, photos, point clouds, measurements, and notes together, it becomes easier to compare them with road ledger annex maps and road base map information. Keeping on-site data in a form that can later be overlaid onto drawings or maps leads to more efficient update work.

Also, when sharing survey results, it is important to organize them so that non-specialist stakeholders can understand. Road information contains many technical terms, and words such as registry-attached maps, road base map information, mapped sections, distance markers, and road areas may be difficult for people unfamiliar with them to grasp. By concisely summarizing which materials were consulted, what can be learned from them, and what needs to be confirmed on site, internal coordination and external consultations can be facilitated.

The National Road Base Map and related databases are effective as an entry point for verifying road information, but the ultimate quality is determined by how verification results are recorded and linked to field checks and update work. Treating database checks, comparison with existing materials, field measurements, and result compilation as a continuous workflow is the practical procedure for accurately utilizing road information.

Summary: Verify road information by combining databases and on-site measurements

When investigating road information using the National Road Base Map and related databases, the starting point is to first understand the nature of the information you can confirm and to clarify your intended use. From there, identify the target location on the map, check the road ledger attached maps and the mapped sections, and interpret the road structure while switching layers of the road base map information. Furthermore, it is important to cross-check with existing materials and on-site conditions, record the verification results, and link them to ledger updates, design, maintenance and management, consultations, and field surveys.

In practice, be careful not to take the information visible in a database as the final judgment. Road information should be interpreted according to the time of creation, update status, scope of maintenance, on-site changes, and its relationship with management documents. Even if a road alignment appears well formed on the screen, its condition on site may have changed due to improvement works, repairs, encroachments, or changes in roadside land use. Conversely, even if information appears insufficient on the screen, the necessary details may be supplemented by the manager’s records or by on-site surveys.

To use the National Road Base Map and related databases effectively, it is important to treat the task of searching for road information and the task of confirming it on site as a single, integrated activity. By using the database to confirm the target sections and the locations of materials, collecting photographs and measurement data on site, and then cross-checking them again with drawings and maps, you can more easily improve the accuracy and efficiency of road management. In particular, coordination between desktop checks and on-site verification is essential for updating the road ledger’s attached maps, maintenance management planning, occupancy consultations, and pre-construction surveys.

To make on-site verification more efficient, a system that lets you organize geotagged photos, point clouds, measurements, and notes on the spot is useful. Relying solely on paper drawings and handwritten notes takes time to reconstruct spatial relationships afterward. If the information collected on site can be saved in a form that is easy to cross-check against the maps attached to the road ledger and the road base map information, verification work, report preparation, and decisions about updates will proceed smoothly.

After checking road information in the national road base map and related databases, the next task is to accurately grasp on-site conditions and organize the data so it can be used for road management. By cross-checking public databases, existing documents, site photographs, and survey results, you can reduce misreadings of materials and discrepancies with actual conditions, making it easier and safer to apply road information in operations.