Where to Search First: Reading Rugged Terrain With LiDAR Slope and Aspect Maps
Updated: 5 days ago
When a missing-person case, suspected body-disposal location, or trace-evidence search involves wooded, rugged, or poorly mapped ground, the hardest problem is often not collecting data. It is deciding where to start.
LiDAR Point Cloud Slope and Aspect maps can help answer that question.
LiDAR Point Cloud Slope and Aspect analysis can reveal subtle terrain features beneath tree canopy, including micro-trails, benches, drainage corridors, and changes in ground steepness that may be difficult to recognize in standard aerial imagery.
By filtering a LiDAR point cloud to create a bare-earth digital elevation model (DEM), analysts can expose subtle terrain beneath tree canopy: micro-trails, old two-tracks, drainage crossings, benches, cut banks, berms, borrow pits, shallow ravines, and other ground features that may be difficult—or impossible—to interpret from standard aerial imagery alone.
The next step is to derive slope and aspect from that terrain model.
Together, those layers can make the landscape more understandable, more searchable, and more useful when combined with the actual facts of a case.
What slope tells us
A slope map shows how steep the ground is at each location. In a terrain model, slope is generally expressed in degrees, from 0° on level ground to 90° at a vertical surface.
For field operations, slope is not simply a visual product. It is an indicator of:
Likely walking difficulty and travel time.
Terrain that may channel travel along a contour, ridge, drainage, road, or trail.
Areas that may be difficult to access while carrying equipment or moving an object.
Places that could create a fall hazard, concealment opportunity, or obstacle to a ground team.
Subtle trail segments that are more likely to be used because they follow comparatively manageable ground.
A seemingly small change in slope can matter. A narrow bench, sidehill trail, abandoned access road, or wildlife path may not be obvious in conventional imagery, but it can become visible in a high-resolution LiDAR-derived elevation surface and slope rendering.
This is especially valuable under mature canopy, where optical aerial imagery primarily records the tops of trees rather than the terrain below them.
What aspect adds
Aspect answers a different question: Which direction does the ground face?
Aspect is the compass direction of the downhill-facing slope, measured clockwise from north:
Aspect value | Downslope direction |
0° or 360° | North |
90° | East |
180° | South |
270° | West |
Flat ground has no meaningful downslope direction and is commonly assigned a special value such as -1 or NoData.
In practical terms, aspect gives each slope face a directional identity. A micro-trail may run along a southwest-facing hillside, cross a north-facing drainage, or follow an east-facing cut bank. When paired with slope, the analyst can determine not only that terrain is steep, but also how it is oriented.
That distinction can matter when evaluating:
Whether a route follows or crosses a hillside.
The direction water, debris, or surface runoff may move.
The likely location of shaded versus sun-exposed terrain.
Differences in vegetation, snow persistence, moisture, soil conditions, and seasonal visibility.
Whether an access route is on the uphill or downhill side of a feature.
How a person moving through the terrain may have encountered obstacles, drop-offs, drainage lines, or terrain funnels.
Slope provides the magnitude of terrain change. Aspect provides the direction. An aspect-slope product combines both so that a viewer can interpret steepness and orientation at the same time.
Seeing micro-trails differently
Micro-trails are often not “trails” in the recreational-map sense. They may be faint walking paths, informal access routes, old utility alignments, deer paths, logging remnants, field boundaries, or repeated travel corridors that have subtly altered the terrain.
A LiDAR-derived DEM can make these features stand out because it models the ground surface after vegetation classification and filtering. From that surface, hillshade, slope, local relief, curvature, and aspect products can reveal patterns that a single map layer may hide.
For example, a faint horizontal line on a hillside may be easier to recognize when:
A hillshade reveals its small cut-and-fill form.
A slope map separates the relatively flatter tread from the steeper hillside around it.
Aspect shows the trail’s relationship to the slope face.
A high-resolution orthomosaic or field imagery layer provides current surface context.
Roads, known access points, parcel boundaries, water features, and case locations are displayed alongside the terrain.
The goal is not to treat every linear feature as a route of evidentiary significance. The goal is to identify features that deserve field verification and to place them in the context of access, movement, and known case facts.
“People go where they know”—with an important caveat
There is a practical investigative principle behind this type of mapping: people often operate within places they know, places they can access, and routes that make sense to them.
That principle should not be oversold as a universal rule. Every missing-person and disposal case is different, and search strategy must remain grounded in the circumstances, evidence, and command structure of the individual investigation.
However, research on homicide body-disposal patterns does support the value of examining areas familiar to an offender. An FBI serial-murder research report describes “hunting areas” as locations offenders identify, become familiar with, and later use. Research summarized from closed homicide cases also found that body locations were often connected to the offender’s property, neighborhood, workplace, or other areas of familiarity; those familiar areas can include routine travel corridors between them.
For missing-person searches, terrain and mobility are also well-established considerations. Search-planning research has found that mobility models can account for terrain slope, vegetation, travel aids, and travel barriers rather than relying only on simple straight-line distance from the last known point. National Park Service search-and-rescue mapping likewise emphasizes integrating elevation, imagery, vegetation, landforms, and operational information to create a more useful depiction of the search area.
In other words: familiarity and terrain do not replace evidence. They help organize it.
From “anywhere” to prioritized terrain
Humans cannot walk through tree trunks. They generally do not choose dense, tangled vegetation when a reasonable alternative exists. They avoid unnecessary steepness, cliffs, water crossings, unstable ground, and barriers—unless circumstances force them otherwise.
That is why terrain analysis is useful.
Instead of treating a wooded search area as one uniform block, investigators can evaluate it as a landscape of relative movement cost and opportunity:
More passable versus less passable ground.
Ridge, contour, drainage, and access-road travel corridors.
Dense vegetation and physical barriers.
Steep side slopes, ravines, cliffs, wetlands, and water crossings.
Faint routes and terrain benches that may support foot travel.
Areas close to roads, tracks, parking locations, residences, workplaces, or other case-specific anchors.
Locations where terrain and vegetation could provide concealment, while still being reachable.
One study of homicide disposal locations found that, where victims were moved from a vehicle at a disposal site, the most frequent movement distance from a road or track was 10 meters, and no victim in that dataset was found more than 61 meters from a road or track. The authors cautioned that relationships and circumstances matter, but the findings illustrate why access features should be evaluated carefully rather than assuming a subject moved deeply into inaccessible terrain.
The practical question becomes:
They could be anywhere—but given the terrain, access, vegetation, and available case facts, where is travel or placement more plausible, and where is it materially less plausible?
A map is strongest beside other maps
To a layperson, a detailed slope-and-aspect rendering can initially look overwhelming. That is normal. A dense palette of colors, small terrain forms, and multiple overlays may not be immediately intuitive.
The solution is not to simplify the analysis until it loses value. The solution is to explain it clearly and pair it with familiar information.
A strong investigative map package might include:
A simple location overview showing roads, parcels, water, known points, and the broader search area.
A hillshade or LiDAR bare-earth model that makes terrain features visible.
A slope map identifying relative terrain difficulty.
An aspect map showing the downhill-facing direction of slopes in degrees.
An aspect-slope composite for interpreting slope direction and steepness together.
High-resolution imagery for current surface conditions and recognizable landmarks.
Known trails, roads, driveways, gates, bridges, culverts, utility corridors, and access points.
Case-relevant locations, such as the last known point, residences, employment sites, phone or vehicle data, witness observations, and prior search coverage.
Field-verification points identifying micro-trails, benches, drainage crossings, suspicious anomalies, or likely access routes.
When displayed side by side, these layers help turn a technically sophisticated terrain product into a practical discussion tool for investigators, search managers, and ground teams.
Important limits
LiDAR terrain analysis is a prioritization and visualization tool—not a substitute for field investigation, evidence processing, search-management protocols, or case-specific behavioral analysis.
A few cautions matter:
A terrain feature is not proof of human use.
Aspect is most useful where there is enough slope to define a meaningful downhill direction; flat terrain has no reliable aspect.
Dense brush, downed timber, seasonal vegetation, flooding, snow cover, and recent land disturbance can change real-world passability.
A path visible in LiDAR may be historic, animal-made, abandoned, or impassable today.
A search plan should integrate terrain analysis with legal authority, safety planning, subject profile, witness information, digital evidence, access constraints, and established search-management methods.
The value of the map is not that it claims certainty. Its value is that it provides a transparent, repeatable way to explain why some terrain deserves earlier attention than other terrain.
The takeaway
LiDAR gives investigators the ability to see the ground beneath vegetation. Slope shows where the terrain becomes difficult. Aspect shows which way that terrain faces. Together, they reveal subtle travel corridors and terrain constraints that are often hidden in standard imagery.
For missing-person cases, suspected disposal sites, and trace-evidence searches, that can help teams make more informed decisions about where to search first, where access is most plausible, and where the terrain itself makes a location less likely.
It is a way to move beyond the broad statement that “they could be anywhere.”
They could be anywhere—but terrain, access, vegetation, familiarity, and case facts can help identify where “anywhere” is most worth looking first.
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About the Author:
Earl Bakke is a Level II Certified Thermographer and FAA Part 107 pilot with night-operations authorization. Twenty years in law enforcement and crash reconstruction, 450+ thermal inspections, and testimony in criminal and civil proceedings. Earl is a consultant and volunteer with the National Center for Missing and Exploited Children. He founded ScenePhoto360 in Stillwater, Minnesota. Read the full background.
