Gis

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GIS

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Geographic Information System - links locational and attribute information and enables a person to visualize patterns, relationships, and trends.

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5 components

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Hardware, software, data, methods, user.

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Layers

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Collections of like data (features) grouped into a single display "entity" which can be manipulated independently of other groups (layers)
-Same base map / coordinate system / overlap other layers

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Discrete Features

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Individually distinguishable. Do not exist beyond observation points (e.g. wells, roads.)

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Continuous Features

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Exist beyond observation points / are continuous in space (e.g. elevation, precipitation, temperature).

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Attribute data

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Descriptive data linked to and associated with location data; may include information such as population sizes, age, names, or titles.

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Spatial Data

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Data that describes the distribution of objects or characteristics on the Earth's surface. Spatial data allows for the placement of layers on a map. Can be discrete or continuous.

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Vector Data

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Discrete data, uses 3 major feature classes (points, lines or polygons) to display discrete data.

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Points

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Nodes, zero dimensionality. Defined by x, y coordinates.

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Lines (polylines)

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Arcs that connect points. 1 dimension, defined by a minimum of 2 nodes.

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Polygon

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Defined as the area within a series of connected (and closed) lines. 2 dimensional.

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Raster Data

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Grid data, represented as a series of cells/as a grid (rows and columns) across continuous space. Each layer generally contains one attribute.

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Resolution

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Refers to the space occupied by each cell. Higher resolution images / rasters have cells that cover less space (e.g. 1 meter vs. 30 meter pixels)

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Geographic Coordinate System

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Defines a point on Earth using a 3-dimensional spheroid (x,y,z)

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Datums

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Reference points that define the position of the spheroid relative to the center of the Earth.

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Maps

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Any concrete or abstract representation of the feature that occur on or near the center of the earth or other celestial bodies in TWO dimensions.

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Map Projection

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An attempt to portray the features of the curved Earth's surface on a flat map.---Generally involves some sort of distortion.

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Digital Elevation Models (DEMs)

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A representation of ground elevation / topography. Cells contain elevation data, usually in meters above sea level. Can be rendered in 3-D or color coded. Raster data.