GISP-E flashcards

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 defined by x,y coordinate pairs, with attributes stored in a linked table. Each feature has explicit geometry and can carry many attributes.

Raster data model

Stores space as a rectangular grid of cells, each holding one value for one theme. Cell size sets resolution, and a single raster layer cannot hold multiple attributes per cell.

Topology

A set of rules describing spatial relationships such as adjacency, connectivity, and containment, stored independently of exact coordinates. It detects gaps, overlaps, and dangling lines that geometry alone does not reveal.

Map projection

A mathematical transformation from the curved Earth surface to a flat plane. Every projection distorts shape, area, distance, or direction, so the choice depends on the map's purpose and extent.

Conformal projection

Preserves local angles and therefore small shapes, making it suitable for navigational and topographic maps. Area is distorted, increasingly so away from the standard parallels or central meridian.

Equal-area projection

Preserves area so regions compare correctly in size, which suits thematic maps of density or totals. Shapes and angles are distorted, especially near the map edges.

Datum

Defines the ellipsoid and its position relative to Earth's center, anchoring geographic coordinates. Mismatched datums between layers shift features by tens to hundreds of meters.

UTM zone

One of 60 six-degree-wide longitude bands using the transverse Mercator projection, with a central-meridian scale factor of 0.9996. Distortion grows beyond about three degrees from the central meridian.

Geographic coordinate system

Locates positions using longitude and latitude in angular units on a defined datum. Distances in degrees vary with latitude, so area and length calculations require a projected system.

Buffer geoprocessing

Creates polygons at a specified distance around input features. The distance uses the layer's coordinate units, so geographic layers need projection or geodesic methods for metric buffers.

Spatial join

Appends attributes from one layer to another based on a spatial relationship such as intersect, within, or closest. The target layer retains its geometry, and match options control one-to-many cases.

Slope and aspect

Slope is the maximum rate of elevation change from a cell to its neighbors, in percent or degrees. Aspect is the downslope compass direction, with flat cells usually coded -1.

Flow accumulation

Counts upstream cells draining into each cell after flow direction is computed. High accumulation values trace stream channels and support watershed delineation with a threshold.

Inverse distance weighting

A deterministic interpolator averaging sample values weighted by inverse distance to a power. It is exact at sample points, cannot exceed the sample range, and creates bull's-eye patterns near clustered points.

Kriging

A geostatistical interpolator using a fitted variogram (nugget, sill, range) to model spatial autocorrelation. It provides a prediction standard error surface, unlike deterministic methods such as IDW.

Moran's I

A global statistic measuring spatial autocorrelation. Positive values near one indicate clustering of similar values, negative values indicate dispersion, and values near the expected value suggest randomness.

Hot spot analysis

Getis-Ord Gi* returns a z-score for each feature indicating clustering of high or low values. Significance requires the paired p-value; the z-score alone does not establish a hot spot.

Map algebra

Raster analysis combining layers with local, focal, zonal, or global functions. Results depend on environment settings, especially processing extent, cell size, and analysis window.

Zonal statistics

Summarizes raster cell values within each zone defined by another dataset, producing counts, means, sums, or similar statistics per zone. Zones and value rasters must share a compatible grid.

Positional accuracy

The closeness of stored coordinates to true ground position, usually reported as a tested root-mean-square error. It is documented separately from attribute accuracy and completeness.

Lineage

Metadata recording source data, processing steps, and parameters used to create a dataset. Without lineage a derived layer cannot be reproduced or defended in a quality dispute.

Minimum mapping unit

The smallest feature area or length retained when a map is compiled at a given scale. Features below the threshold are dropped or merged, so counts differ between scales.

Visual variables

Graphic properties used to encode data: size, shape, value, hue, saturation, orientation, and texture. Hue suits nominal categories, while value and size suit ordered or numeric data.

Natural breaks classification

A classification method placing class breaks where data values cluster, minimizing within-class variance. It suits unevenly distributed data but breaks are not comparable across different datasets.

Quantile classification

Assigns an equal number of features to each class. It emphasizes rank rather than value, so classes may span very different numeric ranges and similar values can fall in different classes.

Metadata standard

A defined structure for documenting geospatial data, such as ISO 19115 or the FGDC standard. It covers identification, quality, lineage, spatial reference, distribution, and entity definitions.

Scale ratio

The ratio of map distance to ground distance, written as 1:n. A smaller n shows more detail; data captured at 1:100,000 should not be presented as accurate at 1:12,000.

Primary and foreign keys

A primary key uniquely identifies each row in a table. A foreign key in another table references that key, implementing one-to-many relationships when placed on the many side.

Normalization

The process of structuring relational tables to reduce redundancy. First normal form removes repeating groups, second removes partial key dependencies, and third removes transitive dependencies.

Geodatabase relationship class

An association between two object or feature classes with defined cardinality. Simple relationships link independent objects; composite relationships make one object's lifetime depend on the other.

Geodatabase versioning

Allows multiple editors to work on separate versions of the same data. Reconciling compares versions, and conflicts occur when the same feature is edited in both.

OGC WMS versus WFS

WMS returns rendered map images with no feature attributes, while WFS returns vector features with geometry and attributes. Choose WMS for display and WFS for analysis or editing.