GIS Fundamentals: Data, Raster–Vector Models & Projections

[GIS basics] What is GIS?

Geospatial Information System: an approach and set of tools for analyzing and mapping geospatial information.

[GIS basics] What is geospatial information?

Data describing how a property varies across space, such as elevation or land-cover type.

[GIS basics] What is quantitative geospatial data?

Numerical values, such as elevation or surface temperature.

[GIS basics] What is qualitative geospatial data?

Categories, such as water, forest, or urban land cover.

[GIS basics] What is location in GIS?

Absolute position of a feature, often specified by latitude and longitude.

[GIS basics] What is geometry in GIS?

The shape of a spatial feature.

[GIS basics] What is topology in GIS?

Spatial relationships such as connectivity, crossings, and adjacency.

[GIS basics] What is an attribute in GIS?

Additional information attached to a spatial feature, such as land use.

[GIS basics] What can GIS analyze?

Co-location, spatial patterns, and relationships among multiple geographic datasets.

[GIS basics] Name two GIS software packages from lecture.

ArcGIS and QGIS; Google Earth Pro is a simpler alternative discussed in class.

[GIS basics] What is a GIS layer?

One spatial dataset that can be displayed, hidden, and combined with other layers.

[GIS basics] What is a basemap?

A reference map or imagery layer underneath additional GIS data.

[GIS basics] What is spatial analysis?

Using location and geometry to investigate spatial relationships, distances, overlaps, and patterns.

[GIS basics] What is a GIS buffer?

An area within a specified distance of a feature; lecture example: valleys within 5 km of an outlet.

[GIS basics] Why must layers use compatible coordinate systems?

Otherwise features may not align, and measurements or spatial comparisons may be wrong.

[GIS basics] What map elements does the lecture emphasize?

Scale, a meaningful color ramp for continuous raster values, and a legend for features/classes.

[GIS basics] What does map scale communicate?

The real-world size or distance represented on a map.

[GIS basics] What is a color ramp?

A sequence of colors representing continuous data values, such as elevation.

[GIS basics] What is a map legend?

A key explaining symbols, features, and categories on a map.

[Raster and vector] What is raster data?

A regular grid of pixels/cells, each storing one or more values.

[Raster and vector] What is vector data?

Geographic features represented mathematically by points, lines, and polygons.

[Raster and vector] What is a vector point?

A single X/Y location, such as a placemark.

[Raster and vector] What is a vector line?

Connected points or a mathematical path, such as a river.

[Raster and vector] What is a vector polygon?

An enclosed area, such as a lake or land parcel.

[Raster and vector] What is a vertex?

A coordinate point defining part of a line or polygon boundary.

[Raster and vector] How can a circle be represented as vector geometry?

By a center coordinate and radius, rather than only straight-line segments.

[Raster and vector] What are two information types stored with vector features?

Geometry (shape, length, area) and user-defined attributes.

[Raster and vector] Why do vectors not become pixelated when zoomed in?

They are mathematical geometries, not fixed pixel grids.

[Raster and vector] What does each raster pixel contain?

A spatial location (pixel center) and a value or category.

[Raster and vector] What is raster spatial resolution?

The physical ground size of one pixel, often stated as meters per pixel.

[Raster and vector] Which is higher resolution: 2 m/pixel or 20 m/pixel?

2 m/pixel: smaller cells capture finer spatial detail.

[Raster and vector] Why can rasterization lose detail?

One cell value represents a finite ground area, simplifying variation within that area.

[Raster and vector] What is a continuous raster?

A grid representing smoothly varying quantities such as elevation or temperature.

[Raster and vector] What is a discrete/categorical raster?

A grid of class codes, such as 1=water and 2=building.

[Raster and vector] Which data structure is natural for a road centerline?

A vector line.

[Raster and vector] Which data structure is natural for a satellite image?

A raster grid.

[Raster and vector] Can land cover be represented by raster or vector?

Yes; coded raster cells or vector polygons can represent categories.

[Raster and vector] Raster vs. vector in one sentence?

Raster stores values in grid cells; vector stores mathematical spatial features.

[Coordinates and projections] What is a geographic coordinate system (GCS)?

A reference system locating positions by latitude and longitude on an Earth model.

[Coordinates and projections] What is a projected coordinate system (PCS)?

A mathematical conversion from geographic coordinates to flat Cartesian X/Y coordinates.

[Coordinates and projections] What coordinate units characterize GCS vs. PCS?

GCS uses angular latitude/longitude; PCS uses planar X/Y, commonly in meters.

[Coordinates and projections] What is a geodetic datum?

The reference ellipsoid and its positioning/orientation used to locate coordinates.

[Coordinates and projections] What is an ellipsoid?

A smooth flattened-sphere approximation of Earth used in coordinate reference systems.

[Coordinates and projections] What do WGS 84 and NAD 83 refer to?

Two common geographic reference systems/datums with slightly different definitions.

[Coordinates and projections] Why might WGS 84 and NAD 83 coordinates differ?

Their reference frames and ellipsoid definitions are not identical; transformations may be required.

[Coordinates and projections] Why do we need map projections?

Earth is curved; maps are flat and require mathematical coordinate transformation.

[Coordinates and projections] What must every flat map projection introduce?

Some distortion of angle/shape, area, distance, or direction.

[Coordinates and projections] What is a cylindrical projection conceptually?

Projecting Earth onto a cylindrical surface.

[Coordinates and projections] What is a conic projection conceptually?

Projecting Earth onto a cone.

[Coordinates and projections] What is an azimuthal/planar projection conceptually?

Projecting Earth onto a plane.

[Coordinates and projections] What are standard parallels?

Lines where a projection surface intersects/touches the Earth model and local scale distortion is absent along those lines in the lecture framework.

[Coordinates and projections] What is a conformal projection?

A projection that preserves local angles and small shapes.

[Coordinates and projections] What is an equal-area projection?

A projection that preserves areas.

[Coordinates and projections] What is an equidistant projection?

A projection that preserves specified distances from designated point(s) or line(s), not all distances everywhere.

[Coordinates and projections] What is a retroazimuthal projection?

A projection preserving direction from map locations toward a designated central point.

[Coordinates and projections] Which projection property is essential for comparing lake areas?

Equal-area.

[Coordinates and projections] What is Tissot's indicatrix?

A visualization of map distortion using projected shapes of originally equal small circles.

[Coordinates and projections] Why use a local rather than global projection?

To minimize distortion over the particular study region.

[Coordinates and projections] What is UTM?

Universal Transverse Mercator: a system of 60 longitudinal zones designed for local mapping.

[Coordinates and projections] Which UTM zone contains Austin, Texas?

Zone 14N, as stated in the GIS lecture.

[Coordinates and projections] What happens if differently projected layers are not transformed properly?

Their locations can be misregistered and spatial analysis becomes unreliable.

[Coordinates and projections] Does every PCS have an associated GCS?

Yes, as emphasized in the lecture.

[Remote sensing and EM] What is remote sensing?

Measuring a property without a sensor physically contacting the object or phenomenon.

[Remote sensing and EM] What types of energy can remote sensing use?

Usually electromagnetic radiation; also sound (SONAR) or gravity variations.

[Remote sensing and EM] What is the SI unit of energy?

Joule (J).

[Remote sensing and EM] What is electromagnetic radiation?

Energy that propagates as electromagnetic waves.

[Remote sensing and EM] What is wavelength (λ)?

Distance between adjacent wave peaks or troughs.

[Remote sensing and EM] What units measure wavelength?

Length units such as meters, nanometers, and micrometers.

[Remote sensing and EM] How many meters are in 1 nanometer?

1 nm = 10^-9 m.

[Remote sensing and EM] How many nanometers are in 1 micrometer?

1 µm = 1000 nm = 10^-6 m.

[Remote sensing and EM] How does visible light relate to electromagnetic radiation?

Visible light is only the portion of the EM spectrum detectable by human eyes.

[Remote sensing and EM] What is white light?

A combination of many visible wavelengths.

[Remote sensing and EM] Why do objects appear colored?

They reflect particular visible wavelengths more strongly than others.

[Remote sensing and EM] Why do non-visible wavelengths help remote sensing?

Materials interact differently with wavelengths outside human vision, revealing additional properties.

[Remote sensing and EM] What is passive reflectance sensing?

Measuring radiation from an external source (usually sunlight) reflected by a surface.

[Remote sensing and EM] Give passive reflectance examples from lecture.

Daytime camera, Landsat, Sentinel-2, and MODIS.

[Remote sensing and EM] What is passive emission sensing?

Measuring radiation naturally emitted by a surface.

[Remote sensing and EM] Give passive emission examples from lecture.

Thermal infrared imaging and SMAP soil-moisture radiometry.

[Remote sensing and EM] What is active remote sensing?

A sensor transmits energy and measures its return.

[Remote sensing and EM] Give active remote sensing examples.

LiDAR and RADAR.

[Remote sensing and EM] A daytime camera measuring reflected sunlight is which type?

Passive reflectance.

[Remote sensing and EM] A thermal camera measuring emitted heat radiation is which type?

Passive emission.

[Remote sensing and EM] A radar transmitting a pulse and detecting its return is which type?

Active remote sensing.

[Remote sensing and EM] What is a remote sensing platform?

The object carrying a sensor, such as a car, UAV, aircraft, or satellite.

[Remote sensing and EM] How can satellites collect observations across the planet?

Earth rotates beneath their ground tracks, helping sensors cover different surface locations.

[Remote sensing and EM] What is a satellite ground track?

The path on the planetary surface beneath an orbiting satellite.

[Topography] What is topography?

The elevation and form of a planetary surface.

[Topography] What is elevation?

Height relative to a specified reference surface or vertical datum.

[Topography] What is relief?

Difference between the highest and lowest elevations in a region.

[Topography] What is a DEM?

Digital Elevation Model: a raster in which each pixel contains an elevation.

[Topography] What is a contour line?

A line connecting locations of equal elevation.

[Topography] What do closely spaced contours indicate?

A steep slope.

[Topography] What do widely spaced contours indicate?

A gentle slope.

[Topography] What is a vertical datum?

The reference surface used as zero for elevation measurements.

[Topography] What is mean sea level (MSL)?

A conventional reference for Earth elevations; its shape is related to the geoid.

[Topography] What is the geoid?

An Earth gravity equipotential surface approximating undisturbed mean sea level.

[Topography] What is an ellipsoidal height?

Height referenced to a reference ellipsoid.

[Topography] What is an orthometric height?

Height referenced to a geoid model.

[Topography] Which vertical datum type is most common on Earth in the lecture?

Orthometric, referenced to a geoid model.

[Topography] What is NAVD 88?

North American Vertical Datum of 1988, given as an Earth orthometric datum example.