GISI Foundation flashcards
GISI Foundation · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Vector data model
- Represents geographic features as points, lines, or polygons with explicit coordinates and attributes, suited to discrete objects with precise boundaries such as parcels, roads, and wells.
- Raster data model
- Represents space as a grid of equally sized cells, each storing one value, suited to continuous phenomena such as elevation, temperature, and imagery.
- Topology
- A set of rules describing spatial relationships such as adjacency, connectivity, and containment independently of coordinates, enabling network tracing and neighbor queries without recomputation.
- Raster resolution
- The ground dimensions represented by one raster cell. Halving cell size quadruples cell count and storage, trading precision against data volume and processing time.
- Map scale
- The ratio of distance on the map to distance on the ground. Large-scale maps show small areas in high detail; small-scale maps show large areas in less detail.
- Geographic coordinate system
- A reference system locating positions on a datum-defined ellipsoid using angular units, typically longitude and latitude in degrees, without flattening the earth.
- Projected coordinate system
- A reference system that applies a map projection and datum to express positions on a plane in linear units such as meters or feet, enabling distance and area measurement.
- Conformal projection
- A projection preserving local angles and small shapes, used for navigation and topographic mapping. Area is distorted, increasingly so away from the standard parallels or central meridian.
- Equal-area projection
- A projection preserving area relationships across the map, used for thematic mapping and density analysis. Shapes and angles are distorted as a tradeoff.
- UTM zone
- One of 60 six-degree-wide Transverse Mercator zones, each with a central meridian scale factor of 0.9996, giving metric coordinates with low distortion within the zone.
- Web Mercator
- A spherical Mercator projection on WGS84 coordinates, widely used for web tiling. It distorts area strongly at high latitudes and is unsuitable for measurement.
- Datum transformation
- A mathematical conversion between two geodetic datums using published parameters. It introduces residual error, unlike reprojection between projections sharing one datum.
- Spatial index
- A data structure such as an R-tree or grid that stores feature bounding boxes, letting a database quickly filter candidates before applying exact geometry predicates.
- Simple Features
- An OGC standard geometry model defining Point, LineString, Polygon, and multi-part types with spatial predicates such as intersects, contains, and touches, implemented by most spatial databases.
- ST_Within versus ST_Contains
- ST_Within(A, B) is true when A lies entirely inside B; ST_Contains(B, A) expresses the same relationship. The two predicates are logical inverses.
- Shapefile limitations
- A shapefile holds one geometry type, caps field names at ten characters, lacks true curves, and stores no topology, duplicating shared boundaries between adjacent polygons.
- GeoJSON
- A text format encoding vector geometry as longitude-latitude arrays in WGS84 with attributes, supporting only two-dimensional geometry and no topology.
- Clip versus intersect
- Clip cuts input features to a boundary while keeping only the input layer's attributes; intersect keeps the overlapping portions of both layers with attributes from each.
- Buffer distortion
- Buffering in a geographic coordinate system measures distance in degrees, producing distorted rings. Project to linear units or use a geodesic buffer for accurate distances.
- Spatial join
- An operation transferring attributes from one layer to another based on a spatial relationship such as intersects or nearest, potentially creating multiple output rows per input feature.
- Dissolve
- A geoprocessing operation merging features that share attribute values into single geometries, optionally computing aggregate statistics, commonly used before summarizing area or length.
- Slope and aspect
- Terrain derivatives from a digital elevation model: slope is the magnitude of the elevation gradient, aspect its compass direction. Flat cells have undefined aspect.
- Viewshed
- An analysis marking cells visible from an observer location given elevation and earth curvature, producing a binary visibility surface rather than a distance measure.
- Map algebra
- A framework applying cell-by-cell expressions across aligned raster grids. Misaligned extents or cell sizes require resampling, which alters original cell values.
- Choropleth mapping rule
- Choropleth maps should encode rates, ratios, or densities rather than raw counts, because differing polygon areas otherwise dominate the visual pattern.
- Color scheme selection
- Sequential schemes suit ordered data, diverging schemes suit values around a meaningful midpoint, and qualitative schemes suit unordered categories with no inherent order.
- Map classification methods
- Equal interval, quantile, natural breaks, and standard deviation divide the same data differently, changing the map's appearance; the method should be stated in the legend.
- Figure-ground contrast
- The visual separation between thematic data and basemap, achieved by muting basemap saturation and value so the data layer reads in front of background context.
- Positional accuracy
- A data quality element describing how closely mapped coordinates match true ground positions, commonly summarized by root mean square error against independent checkpoints.
- Metadata standard ISO 19115
- An international standard defining geospatial metadata content, covering identification, lineage, spatial reference, accuracy, contact, and use constraints for datasets.
- Data lineage
- Documentation of source data, processing steps, and parameters used to produce a dataset, enabling reproduction of results and tracing of errors to their origin.
- Locational privacy
- The ethical obligation to protect individuals' location information through aggregation, masking, or access controls, and to avoid publishing data that could identify them.