CMPS GIS
Understanding Maps and Geographic Data Management
Compass GIS users may consider maintaining their own GIS data. Other users might want to gain in depth understanding of maps and geographic data management. Whatever the case, these basic cartographic terms are essential to anyone who is willing to undertake that kind of tasks. Let’s take a look at them:
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What is the Meaning of Geographic Data?
Also known as geospatial data or geographic information, it is the data or information that identifies the geographic location of features and boundaries on Earth, such as natural or constructed features, oceans, and more. Spatial data is usually stored as coordinates and topology, and is data that can be mapped.
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What Is the Difference Between Vector and Raster Data?
In GIS, vector and raster are two different ways of representing spatial data. However, the distinction between vector and raster data types is not unique to GIS.
Raster data is made up of pixels (or cells), and each pixel has an associated value.
Vector data models are representations of the world using points, lines and polygons. Vector models are useful for storing data that has discrete boundaries, such as country borders, land parcels, and streets.
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What Is a Datum?
In surveying and geodesy, a datum is a set of reference points on the earth’s surface against which position measurements are made, and (often) an associated model of the shape of the earth (reference ellipsoid) to define a geographic coordinate system.
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What Is a Coordinate System?
In geometry, a coordinate system is a system which uses one or more numbers, or coordinates, to uniquely determine the position of a point or other geometric element on a manifold such as Euclidean space.
A point has two coordinate values: latitude and longitude. Latitude and longitude measure angles. Latitude is defined as the angle formed by the intersection of a line perpendicular to the earth’s surface at a point and the plane of the Equator.
A geographic coordinate system (GCS) uses a three-dimensional spherical surface to define locations on the earth. A GCS is often incorrectly called a datum, but a datum is only one part of a GCS. A GCS includes an angular unit of measure, a prime meridian, and a datum (based on a spheroid).
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What Is a Map Projection?
A projected coordinate system based on a map projection such as transverse Mercator, Albers Equal Area, or Robinson, all of which (along with numerous other map projection models) provide various mechanisms to project maps of the earth’s spherical surface onto a two-dimensional Cartesian coordinate plane. All projections will distort either Area or Shape.
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What Is Geocoding?
Geocoding is the process of assigning locations to addresses so that they can be placed as points on a map, similar to putting pins on a paper map, and analyzed with other spatial data. The process assigns geographic coordinates to the original data, hence the name geocoding
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What Is a Network Dataset & How Does the Network Dataset Work?
A network dataset is a GIS dataset that is designed to support network analysis. It typically consists of lines representing the routes of flow in the network, augmented with other features (such as junction points), topology and attributes that model network-relevant properties such as impedance and capacity of flow.
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What Are Attributes?
Attributes describe different characteristics of objects and a table showing the attributes of objects is called an attribute table. Each object corresponds to a row of the table and each characteristic or theme corresponds to a column of the table. Thus, the table shows the thematic and some of the spatial modes.
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What is Nominal Value?
On a nominal scale, numbers merely establish identity. For example: a phone number signifies only the unique identity of the phone. In a race, the numbers issued to racers are used to identify individuals are on a nominal scale and these identity numbers do not indicate any order or relative value in terms of the race outcome. In Compass, the nominal values are present in areas such as Fleet (bus numbers), Student ID’s, Stop ID’s and many others.
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What is Ordinal Value?
In the race, the finishing places of each racer, i.e. 1st place, 2nd place, 3rd place, are measured on an ordinal scale. The numbers mean something relative to each other but we do not know how much time difference there is between each racer. In Compass, ordinal values are the stop sequencing and the routing sequencing of the runs.