# Glossary

Actual Scale (Scale): the scale at any point on a maps surface in relation to the earth (see scale factor and principal scale).

Area of Study (Intro to Geomatics): the geographic extent of the place being studied.

Cartesian coordinates: coordinates indicating location in a space defined by two baselines intersecting one another at right angles. The intersection point is the origin for locations defined by distances along the two intersecting axes.

Choropleth Map (Maps and Mapmaking): A map that assigned to units of analysis a colour or fill pattern based on a classification of numeric data. Areas with similar colours have similar values, dissimilar colours on the map represent dissimilar values.

Colour (remote sensing): each distinguishable variation on an image produced by a multitude of combinations of hue, value and chroma.

Conformal: maps that preserve shapes, although continents will appear relatively larger or smaller than one another their shape will be consistent to their appearance on the earth, or reference globe.

Conic projection: The contact line between the plane and the surface of the globe is a small circle (non-great), the same is true for secant conic projections.

Continuous reference system (coordinate systems): lat./long. or UTM identity for any point on earth’s surface with infinite accuracy.

Cylindrical projection (map projections): the single contact point (line) between the plane surface and the globe is a great circle, except in the case of a secant cylindrical projection in which case the two lines of intersection between the cylinder and globe are equidistant from a great circle. (see following slides for visual).

Developable Surface (map projections): a surface onto which the graticule of Earth is projected. Specifically, a developable surface is one that must be manipulated before and after projection, such as being wrapped around the reference globe and subsequently unwrapped.

Discrete reference system (coordinate systems: system for referencing discrete units on the earth’s surface (Street address, township and range).

Ecological Fallacy (Intro to Geomatics): Drawing conclusions about individuals when only group data is available. If the average income of a group of people is above the national average, it would be an ecological fallacy to conclude that all individuals have above average income.

Equal Area: Areas of shapes (continents, lakes, oceans, countries, etc.) will be consistent with the reference globe and to scale with the earth.

Equidistant (Azimuthal): maps that preserve distances as measured from a central point in any direction. In some cases distances are equal when measured from a circle on the map, if the projection is secant rather than tangent.

Extrapolation (remote sensing): estimating a value that is beyond the range of sampled values (either in a spatial or non-spatial range)

Geocoding: the process of assigning a continuous location reference (global frame of reference) to a discrete object or address.

Geodesy: The science of the earth’s shape and size; also related to measuring the variable gravitational force exerted by the earth. Models of the earth’s size and shape are used to produce datums upon which frames of reference and mapping systems are based.

Geodetic datum: a definition of the size, shape and orientation of the earth; datums support the development of global reference and mapping systems.

Geographic Information Science: The science related to examining and studying the technologies associated with collecting, storing and processing spatial data. The primary purpose is to study and expand the technology.

Geographic Information System: the integrated hardware and software used to collect, store and process spatial data.

Geoid: a model of the earth’s surface (shape) based on the variable gravitational force exerted by the earth as an object.

Georeference: The act of coordinating collected data to a common global reference system, other related topics include geo-coding and address matching.

Gnomic: Map projection with a theoretical light source at the earth’s center.

Graticule: the pattern of intersecting lines (latitude and longitude) on Earth, can also be applied to any spherical, ellipsoidal or geoidal object.

Grid: the pattern of intersecting lines on a flat (2-dimensional) surface.

Image (remote sensing): A reproduction or imitation of the form of a person or thing. The optical counterpart of an object produced by a lens or mirror or other optical system.

Interpolation (remote sensing): estimating a value that is within the range of sampled values, but not one of the sampled values (either in a spatial or non-spatial range)

Interval (levels of information): data is given a value that is based on a fixed scale with no true zero value. The interval between observations is constant, but is not related to an absolute zero (measures of temperature other than Kelvin). Interval data may appear as though it can have complex operation performed on it, such as performing a ratio, multiplying, etc., but this is not true (i.e. 10 degrees C is not twice as warm as 5 degrees C).

Line of tangency: Projection surfaces can come into contact with the globe’s surface or exist some distance away from the surface. When a developable surface comes into contact with the globe’s surface along a single line the projection is considered tangent (the projection surface is tangent to the globe along that line). When a developable surface comes into contact with the globe along two lines the projection is considered secant (the surface “cuts through” the surface of the globe). In the case of a planar projection (non-developed) the projection surface comes into contact with globe at a point for a tangent projection and a small circle for a secant projection. (see following slides for examples)

Nominal: data is put into classes with distinct labels; classes have no relationship to one another and are given no relative value (eye color is an example).

Ordinal: data can be placed in ranked categories, categories are differentiated by their position in the ranked scale, values can be greater or less than one another but the differences cannot be measured (A is taller than B, 1st, 2nd, 3rd, 4th, etc.).

Orthographic: a view of the world from a vertical perspective, as though one were looking at the entire earth from directly above the entire surface at once. Orthographic projections are computed with a theoretical light source placed infinitely far away from the earth.

Pattern (remote sensing): Pattern is the spatial arrangement of objects and is a macro image characteristic.

Photo Interpretation (remote sensing): The act of examining aerial photographs/images for the purpose of identifying objects and judging their significance.

Photogrammetry (remote sensing): The science or art of obtaining reliable measurements by means of photography.

Photography (remote sensing): The art or process of producing images on a sensitized surface by the action of light or other radiant energy.

Planar Projection: the plane onto which the globe’s surface is “projected” is not altered following or preceding projection. The plane is tangent to the globe at a point or along a small circle in the case of a secant projection.

Polar Coordinates: coordinates indicating location in a space defined by a single baseline. One end of the baseline is defined as the origin and locations are  indicated by a distance (in some measurement system) away from the origin and an angular deviation around the origin away from the baseline.

Principal Scale: (scale of globe radius to actual earth radius) scale of the model of the earth being used for a map to the earth. Principal scale and actual scale will be the same all over the reference globe.

Public Particpations GIS (PPGIS): studies related to the societal context of Geographic Information Systems.

Query: question asked of a database.

Ratio (levels of information): data exists on a scale with a constant interval between values and has an absolute 0. Ratio data can be multiplied by a constant, and have a ratio applied to observations, supporting complex analytical operations.

Resolution (remote sensing): Resolution is defined as the ability of the entire photographic system, including lens, exposure, processing, and other factors, to render a sharply defined image. An object or feature must be resolved to be detected and/or identified.

Scale Factor: Actual scale divided by the Principal scale; SF will therefore be 1.0 everywhere on the reference globe. On the projected map surface the SF may be higher or lower than 1.0 due to distortions associated with transforming the reference globe into a flat map.

Site (remote sensing)- How objects are arranged with respect to one another; or with respect to various terrain features.

Spatial Autocorrelation: A measure of the spatial relationship between the occurrence of an attribute in different locations.

Stereographic: Map projection with a theoretical light source at the antipode (opposite side of the earth’s surface being mapped).

Texture (remote sensing): The frequency of change and arrangement of tones. Texture is a micro image characteristic and is related to the visual impression of smoothness or roughness of an area.

Tone (remote sensing): Tone can be defined as each distinguishable variation from white to black.

Topology: For GIS, there are 3 precepts of Topology: 1. Connectivity (of nodes to one another by lines), 2. Area definition (by connecting arcs with nodes and closing polygons), and 3. Adjacency (polygons that share a single arc-boundary are adjacent. Topology contains/records the spatial information that is unchanged by transformation (cartographic transformation).

Unit of Analysis (Intro to Geomatics): the individual units that are used to create an aggregate pattern for an area of study. The unit of analysis might be a single observation (i.e. household income) or a summary of observations (average income for a neighbourhood). Units of analysis are studied or presented together so that a pattern across a larger spatial extent can be communicated.