LEC14 Mapping Notes

Theodolite:
- A precision optical instrument for measuring angles between designated visible points in the horizontal and vertical planes.
- Used to measure horizontal and vertical angles.
EDM (Electronic Distance Measurement):
- A method of determining the length between two points using electromagnetic waves.
- EDM is commonly carried out with digital instruments called theodolites/total stations.

Used to determine horizontal and vertical angles, slope, horizontal and vertical distances, coordinates, and even draft the map.
Records x, y, and z values:
- X: Easting
- Y: Northing
- Z: Elevation

Timed radio transmissions from satellites with accurately known orbits are used to estimate locations of GPS receivers on Earth.
Used for:
- Determining location
- Navigation
- Mapping
- Tracking
- Timing

Technique of obtaining reliable measurements of objects (2D or 3D) from aerial photographs.
Overlapping is necessary for determining parallax and 3D viewing.

Using electromagnetic radiation sensors to record photographs of the environment.
Process of detecting and monitoring the physical characteristics of an area by measuring its reflected and emitted radiation at a distance (typically from satellite or aircraft).
Special cameras collect remotely sensed images, which help researchers "sense" things about the Earth.
Applications:
- Mapping large forest fires from space.
- Tracking clouds to predict the weather or watching erupting volcanoes.
- Tracking the growth of a city and changes in farmland or forests over several years or decades.
- Discovery and mapping of the rugged topography of the ocean floor (e.g., mountain ranges, canyons, and magnetic striping).

LIDAR measures the distance by lighting up a target object and analyzing the reflected light.

Mapping surveys are made to determine the locations of natural and cultural features on the Earth’s surface and to define the configuration (relief) of that surface.
Natural features: vegetation, rivers, lakes, oceans, etc.
Cultural (artificial) features: roads, railroads, buildings, bridges, canals, boundary lines, etc.
Two different types of maps:
- Planimetric: Depicts natural and cultural features in the plan (X-Y) views only. Objects shown are called planimetric features.
- Topographic: Includes planimetric features and shows the configuration of the Earth’s surface (elevation changes and terrain features).

Relief (variations in the elevation of the ground surface) is shown on maps by using various conventions and procedures.
For topographic maps, contours are most commonly used.
Digital elevation models (DEMs) and three-dimensional perspective models are newer methods for depicting relief, made possible by computers.
The majority of maps are produced using computers, Computer-Aided Drafting (CAD) software, and data collectors.

Mapping surveys are conducted by one of two basic methods:
- Aerial (photogrammetric)
- Ground (field) techniques
- Often a combination of both is employed.
Airborne laser mapping systems may also be used.
Ground surveys are commonly used in preparing large-scale maps of smaller areas.
Even when photogrammetry or airborne laser mapping is utilized, ground surveys are necessary to establish control and to field-check mapped features for accuracy.

Map scale is the ratio of the length of an object or feature on a map to the true length of the object or feature.
Map scales are given in three ways:
- By ratio or representative fraction, such as 1:2000 or 1/2000.
- By an equivalence.
- Graphically using either a bar scale or labeled grid lines spaced throughout the map at uniform distances apart.

A map plotted at a scale of 1 in = 200 ft. If distances and locations can be scaled from the map to within say 1/50th in., this represents a scaling error of $(1/50) * 200 = \pm 4$ ft.
Choice of scale depends on the purpose, size, and required precision of the finished map.