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Mapmaking Tools and Technology

Past cartography tools include compasses, mylar sheeting, planimeters, and dividers – all of which are used to create analog maps. As digital mapping has become more popular, modern cartography tools have changed significantly.

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Courtesy of the descendants of Louis F. Cutter

Cartographer, Louis Cutter, used this measuring wheel to calculate mileages along many White Mountain footpaths.  He created this odometer using the front wheel of a bicycle. 

Geodimeter. Courtesy of Squam Lakes Natural Science Center with assistance from Thomas Stepp

For Brad Washburn’s 1968 edition of his Chart of Squam Lake and map of the Squam Range (1973) the Geodimeter was used, along with a theodolite, for establishing an extremely accurate grid of survey “control points.” These were metal discs cemented into rock on, for example, the summits of Mt. Morgan, Rattlesnake Mt., and Red Hill.

“Geodimeter” is an acronym for “Geodetic Distance Meter.”

Theodolite. ourtesy of Squam Lakes Natural Science Center with assistance from Thomas Stepp

A theodolite is a surveying instrument with a fully pivoting telescope which allows it to measure both horizontal and vertical angles. This Kern DKM3 is accurate to within 1/10th of a second of arc. What this means in actual surveying is that over a distance of ten miles the horizontal error would be only 1/3rd of an inch.

For the Squam Lake/Squam Range survey work, the theodolite would have been used both for critical horizontal and vertical angles to important survey stations, and for many of the several thousand other measurements used to establish the shoreline, the depth sounding grid points, and many other details on both maps.

Thomas Stepp

LIDAR Technology

LiDAR stands for Light Detection and Ranging. A LiDAR unit sends out laser light pulses which bounce off of any surface they hit and are reflected back to sensors in the LiDAR unit. The receiver then notes the time it took for the light to travel to the ground and back, and uses the total travel time to calculate the distance to that surface. As the unit moves along a set route, it sends out laser light pulses toward a target, typically the ground. Using Global Positioning System (GPS) information, these distance measurements are transformed into three-dimensional points (termed a “point cloud”), which can then be converted into accurate location and elevation information. This data can be extremely difficult to obtain otherwise.

Crawford Notch. Courtesy of The New Hampshire Geological Survey (NHGS)

LiDAR is also useful in visualizing landscapes that are covered by trees, as we have here in New Hampshire. Laser light pulses return to the LiDAR unit from different surfaces near the ground, including trees, buildings and the earth surface. In a tree-covered area each laser pulse may be reflected off of more than one surface, where part of the beam bounces off of the leaves, and another part of the beam travels further and reflects off of the ground. Later, a LiDAR “point cloud” undergoes processing to remove trees and buildings, revealing details of the ground surface that would not be visible on a regular photograph. The resulting product is called a bare-earth surface.

Franconia Notch. Courtesy of The New Hampshire Geological Survey (NHGS)

The Franconia Notch and Crawford Notch images are bare-earth hillshades. A hillshade is a 3D representation of the Earth’s surface which uses an imaginary light source to cast shadows on a landscape created by LiDAR. By default the light source “shines” from the northwest direction, and from an altitude in the sky of 45 degrees. Sometimes it is useful to change which direction the light is coming from, as this can make subtle features more apparent.

Mount Washington Hill Slope

The Mt. Washington Slope image uses a slope function instead of hillshade to show elevation information. The slope function calculates the difference in height between the pixels, or cells, in an image and then assigns a color value depending on how great the difference is. Usually the greater the elevation difference the darker the color, so a very steep slope is shown as dark gray while a flatter surface will be almost white.

The slope style is used when the information about the steepness of a hillside is important. For example, a person viewing the map would very quickly be able to tell where all of the steep slopes are simply by looking at the darker areas.

Mount Washington Hill Shade

Hillshade is often used when depicting a more natural view that is easy for the viewer to understand, because it represents what a person would see if looking down on the landscape with the Sun shining at an angle on the land.

It is interesting to compare the hillshade and slope function display styles in the same area. If you look at the Mt. Washington Shade image and the Mt. Washington Slope image you can see that even though they show the same region, they look different. The type of display style that is used for a given map depends on the traits that the person creating the map wants to highlight.

The New Hampshire Geological Survey (NHGS), part of the New Hampshire Department of Environmental Services (NHDES), in collaboration with the United States Geological Survey (USGS), the White Mountain National Forest, and the Federal Emergency Management Agency (FEMA), acquired LiDAR data for the entire state during the late 2000s and throughout the 2010s. In addition to providing a critical tool to support resource management, this information is a great way for the public to understand the land around them, from being able to see long-abandoned stone walls deep in the woods, to glacial deposits that can be several miles long.