GIS Comprehensive Material

Raster imagery with 7-bit radiometric resolution can show how many values?  

2^7= 12827= 128

distinct brightness levels. From 0-127 

Ellipsoid 

• Ellipsoid 

• Earth is not a perfect sphere—it's an oblate ellipsoid (flattened at the poles due to rotation) 

• Defined by a major (equatorial) and minor (polar) axis 

• Used to mathematically approximate Earth's shape 

How big and how spherical, but cannot show location 

Datum:  

• A reference system that aligns an ellipsoid and geoid to a real-world location 

• Combines a spheroid (ellipsoid) with a network of measured ground points 

• Provides the precise location of features on the Earth's surface 

• Any shape file or raster file you want to georeference 

• Examples: NAD83, WGS84 

What is a vegetation index in remote sensing? Describe a vegetation index with example?  

Vegetation Index: Mathematical formula that uses reflectance values from different wavelengths (red & near-infrared) to assess the presence, health, and density of vegetation 

Vegetation Index

= 𝑁𝐼𝑅/𝑅𝑒𝑑

 

NDVI

𝑁𝐼𝑅−𝑅𝑒𝑑/𝑁𝐼𝑅+𝑅𝑒𝑑

 

NIR

reflectance in the near-infrared band (healthy vegetation reflects strongly) 

RED

reflectance in the red band (vegetation absorbs for photosynthesis) 

NDVI Range: 

• +0.6 to +1.0 = dense, healthy vegetation 

• ~0.2 to 0.5 = sparse vegetation 

• ~0 or negative = barren areas (urban, water, rock, snow) 

Radiometric Resolution (Color Depth): 

• Measures how finely a sensor detects brightness differences 

• Expressed in bits (e.g., 8-bit = 256 gray levels) 

• Higher = more detail in light/dark variation 

Spectral Resolution (Wavelength Bands): 

• Measures the number and width of bands the sensor records 

• Determines which EM wavelengths (colors) are captured 

• Multispectral = several broad bands (e.g., R, G, B, NIR) 

• Panchromatic = one wide grayscale band (200–700 nm) 

Sun-synchronous polar orbits: 

• Near-polar path; Earth rotates beneath 

• Global coverage with repeat, fixed-time sampling 

• Altitude: 500–1,500 km 

• Ex: Landsat, Terra, Aqua 

Non-Sun synchronous orbits: 

• Flexible over tropics, mid/high latitudes 

• Variable revisit times 

• Altitude: 200–2,000 km 

• Ex: TRMM, ICESat 

Geostationary orbits: 

• Stays fixed over one region (continuous view) 

• Covers low-mid latitudes, ideal for weather 

• Altitude: ~35,000 km 

• Ex: GOES 

Georeferencing: 

• Aligns an image to a known coordinate system 

• Uses transformations like shifting, rotating, or scaling 

• Does not correct for terrain or sensor tilt distortion 

Orthorectification: 

• Geometrically corrects distortions from terrain and sensor angle 

• Produces a true-scale, map-accurate image 

• Essential for precise measurements in varied topography 

 

Georeferencing: 

• Aligns raster/image data to a real-world coordinate system 

• Involves transformation methods (e.g., scaling, warping) 

• Used for scanned maps, aerial photos, etc. 

Geocoding: 

• Converts addresses or place names into geographic coordinates 

• Common in location services and address mapping 

• Often based on reference databases like street networks 

A given satellite has a spatial resolution of 30 m. How many pixels of this satellite will be required to cover a study area of 80 km2  

Spatial Resolution= 30m 

• 30 m X 30 m= 900m² 

Study Area= 80km² 

• 80 X 1,000,000 =80,000,000m² 

Calculation= 80,000,000/ 900= 88,889 pixels  

Equation: Number of pixels= 𝐴𝑟𝑒𝑎 𝑜𝑓 𝑠𝑡𝑢𝑑𝑦/𝐴𝑟𝑒𝑎 𝑝𝑒𝑟 𝑝𝑖𝑥𝑒𝑙

 

Raster: (Pixel) ADVANTAGE

• Simple data structure, easy to process 

• Good for representing continuous data (e.g., elevation, temperature) 

Raster: (Pixel) DISADVANTAGE

• Large file sizes for high resolution 

• Less precise at representing boundaries 

Vector: (point, line, polygon) ADVANTAGE

• Accurate representation of points, lines, and areas 

• Efficient storage for discrete features (e.g., roads, parcels) 

Vector: (point, line, polygon) DISADVANTAGE

• Complex data structure and processing 

• Poor handling of continuous surfaces (e.g., terrain) 

Euclidean distance formula  

Square root of (x₂-x₁)² + (y₂-y₁)²

Conformal

Preserves local shape, but size (area) is distorted (Mercator projection) 

Equal Area:

Preserves the area (proportions) of displayed features, but distorts shapes (Mollweide/ Gall-Peters projection) `

Tangent

Is where the projection surface contacts the globe  

• 1 standard parallel 

Secant:

Projection in which the projection surface intersects the globe 

• More than 1 standard parallel (2) 

 

The Universal Transverse Mercator (UTM) coordinates of a position in northern hemisphere states that its northing is 3,546,453 m N and easting is 400,765 m E. How far is this position from the International date line? 

• Easting= 400,765 m E 

• At equator= 1° longitude = 111.111 km, so 3°= 333.333km = 333,333 m 

• Distance from central meridian= 500,000 – 400,764 m E= 99, 235 m 

• Distance from International date line= 333,333 m + 99,235 m = 432,568 m => 432.5 km 

 

The distance between 1 degrees of longitude is approximately? 

Distance between 1° of longitude= 111.111 km  

Short Integer

-32,768 -32,767 

Long Integer:

-2,147,483,648 - 2,147,483,647 

Float

Decimals values w/ 1-6 decimal places 

Double

Decimals values w/ >6 decimal places 

 Conceptual Generalization:

Mainly effects the semantics (attributes) of the data. The map ledged changes 

• Select/omission of categories 

• (Re)classification 

• (Re)symbolization/ Enhancement 

Graphic Generalization:

It mainly effects the geometry and location of the objects  

• Simplification 

• Enlargement 

• Displacement/Graphic Combination or Selection 

What are isogonic lines and why are they important and useful?  

Lines connecting places of equal magnetic declination- angular distance between magnetic north and true (geographic) north 

• Important for correcting compass readings and navigation 

Thematic Maps: 

• Focus on a specific theme (e.g., population, climate, land use). 

• Display qualitative or quantitative information. 

• Show the spatial distribution of a theme across geographic areas. 

• Types: Dot-distribution, choropleth, isoline, flow maps, proportional circle maps. 

General Purpose/ Atlas Map:

 

 Provide broad geographic information (e.g., cities, roads, physical features). 

• Used for general navigation and reference. 

• Show a variety of features (e.g., political boundaries, physical landmarks). 

• Examples: World maps, political maps, road maps. 

Calculating Real-World Distances Using Map Scale: 

1. Identify the map scale (e.g., 1:50,000). 

2. Measure the map distance (in cm or inches). 

3. Apply the scale: Multiply the map distance by the scale factor. 

Real Distance Formula = Map Distance × Scale Factor 

Example: 
Map scale: 1:50,000 
Map distance: 3 cm 
Real distance: 3 cm × 50,000 = 150,000 cm = 1,500 m 

Euclidean Distance:

Straight line distance, calculated using Pythagorean Theorem= hypotenuse 

Manhattan Distance:

Distance based (horizontal & vertical), like a taxicab route 

Functional Distance:

Measures time, effort, or cost, considering barriers like terrain 

1. Least-cost path: Finds the lowest-cost path considering factors like terrain or obstacles 

Triangulation: 

• Measures angles from a known baseline to distant objects 

• Uses trigonometry to calculate distances 

Trilateration:  

Determines position by measuring distances from multiple satellites. 

GIS Tools: Open Source: 

• Free and modifiable software. 

• Examples: QGIS, GRASS GIS (developed by the US Army Corps of Engineers), and Idrisi (non-profit system, originally raster-based). 

• Open-source tools encourage collaboration and are cost-effective. 

GIS Tools: Proprietary:  

• Commercial software that requires licensing. 

• Examples: ArcGIS (leading desktop GIS by ESRI), MapInfo, GeoMedia, Maptitude, TransCAD (specialized for transportation). 

Volunteered Geographic Information (VGI) 

• VGI is spatial data contributed freely by volunteers, often collected and edited by the general public. 

• Examples: OpenStreetMap, Wikimapia, Flickr, and Foursquare check-ins. 

• Data is typically reviewed for accuracy, and anyone can contribute or edit. 

Datum Shift

Occurs when geographic reference systems (datums) are changed or transformed. 

• Latitude and longitude are only valid with reference to that datum --> Data shift 

• Impact on GIS: 

• Causes positional errors and coordinate mismatches 

• Inaccurate spatial analysis when combining data from different datums. 

• Requires reprojection or transformation to align data correctly. 

What type of distortion increases significantly as you move away from the central meridian in UTM zones?

Scale 

• Moving away from the central meridian. 1:1 

In the State Plane Coordinate System, why are different projections used in different zones?

To minimize distortion 

• Lambert conformal or UTM depending 

• More elongated N-S, divide zones E-W 

What explains why one degree of longitude covers a shorter east-west distance near the poles?

Meridians converge toward the poles  

• The distance between one degree of latitude: 111.111 

• Longitude changes a lot; maximum at equator, minimum at the poles

Which coordinate pair is an example of UTM?

15T 642268 m E, 4852852 m N 

• Northing is 7 digits  

• Easting is 6 digits  

• Every zone gets a false easting of 500,000 

 

What is the major difference between spatial and radiometric resolution in a remote sensing system?

What is the major difference between spatial and radiometric resolution in a remote sensing system?

The visible spectrum used in remote sensing spans approximately

0.4–0.7 μm

What is the typical altitude of a geostationary satellite?

~35,786 km 

Orthorectification of a raster imagery is essentially a 2D rather than 3D transformation

False

• Requires height 3D 

• Georeferencing is 2D transformation 

• Structure from motion:

  • First produced a point cloud 

  • Raster and create a DEM 

  • Last output is an Ortho imagery (overlapping photos)  

    • Stitched together to make a mozaic and needs to be corrected for perspective errors (DEM)- Orthorectification 

Arc (Info) Coverages format can store both raster and vector data

False 

Arc info= e00 files (Vector) 

Which generalization operation involves merging multiple small features into a larger, generalized feature?

Aggregation

What is the difference between true north and magnetic north?

True north points toward the geographic North Pole; magnetic north points toward the Earth’s magnetic field 

1 square kilometer equals exactly 1,000,000 cubic meters

False 

• 1000 m X 1000m = 1,000,000 m2 

Which of the following best describes a key difference between a DEM and a point cloud?

A DEM is a gridded raster surface; a point cloud is an unstructured collection of x, y, z points 

• Point cloud= bathymetric using SONAR 

 

Which data structure is best suited for capturing raw elevation data from LiDAR or photogrammetry?

Point cloud 

• LIDAR and sfm= Point cloud  

• Up to you to decide what you want to do with the point cloud  

• Sfm castle: point cloud FIRST 

• Mesh model --> another name for TIN