# Shared Flashcard Set

## Details

GIS Exam 1
Exam 1
28
Geography
10/28/2015

Term
 Geodesy
Definition
 The science of measuring the shape of the Earth.    The Earth has an irregular shape which affects how we define coordinate systems used to represent geographic features in GIS
Term
 Coordinate System
Definition
 System of locations on a 3-D ellipsoid (Long/Lat). So if we want to do a study that involves analysis of the location, shape or extent of geographic features we need to have a coordinate system.
Term
 The five components tomodel the Earth anddevelop a coordinate system for a flatmap:
Definition
 • Ellipsoid/Spheroid • Spherical or geographic coordinate system • Datum • Projection • Units
Term
 Ellipsoid/Spheroid
Definition
 An ellipse is a 2-dimensional shape that is oval in shape. The shape is similar to a circle but flattened. An ellipsoid is actually a three-dimensional (mathematical) representation of an ellipse; it is created by rotating an ellipse about an axis. Ellipsoids (sometimes called spheroids) provide a model of the shape of the Earth. To georeference something in GIS, we need to define this model.
Term
 Geographic Coordinate System
Definition
 • A reference system used to locate and measure geographic features on the surface of a sphere-like object, like the earth.  Lat/Long, UTMs, Decimal Degrees
Term
 Datum
Definition
 A set of control points whose geometric relationships are known, either through measurement or calculation. Give distance, area, direction, etc. between locations on the Earth.  Earth is not smooth sphere, so different datums work better in different places on the Earth.  Datums have two components: • The reference ellipsoid • A set of survey points. Both the shape of the spheroid and its position relative to the earth are important.  There are two types of datums: (1) Earth-centered and (2) Local.
Term
 Earth-Centered Datum
Definition
 An earth-centered datum establishes the origin of the ellipsoid at the earth's currently known center of mass. Earth-centered datums define an X, Y, and Z, Cartesian coordinate system with respect to the center the reference ellipsoid.
Term
 Local Datum
Definition
 Aligned so that it closely corresponds to the earth's surface for a particular area.
Term
 Projection
Definition
 Represent locations identified in the geographic coordinate system and place them a flat surface (map). Map projections transfer the spherical Earth coordinates onto a twodimensional (planar) coordinate system.  Always has some distortion.
Term
 Distortion
Definition
 Occurs when projecting ellipsoid Earth on a flat surface. Scale, distance, area, and shape can call be changed depending on projection method.
Term
 Units
Definition
 Must be same throughout coordinate systems used, ways of measuring components of maps, and pretty much everything. Keep track and keep similar.
Term
 Graticule
Definition
 A network of lines representing meridians and parallels, on which a map or plan can be represented. Dont meet at right angles on the earth so get distorted when projected flat.
Term
 Project Options
Definition
 • Using a cylinder (Cylindrical)-  Area is true; Shape and scale get distorted near the upper and lower regions of the map. • Using a plane (Planar)- Often used for air route distances. Distances measured from the center are true. Distortion of other properties increases away from the center point.  • Using a cone (Conic)- Distorts scale and distance except along standard parallels. Areas are proportional and directions are true in limited areas.
Term
 Problems with Lat/Long
Definition
 Lat/long graticules dont meet at right angles which means there is distortion when projected flat.
Term
 Map Scale
Definition
 Refers to the relationship (or ratio) between distance on amap and the corresponding distance on the ground. For example, on a 1:100000 scale map, 1cm on the map equals 1km on the ground.
Term
 Vector Data
Definition
 Composed of Points, Lines, and Polygons. Advantages: Same at any scale, easy to use on change coordinate system, easy to read. Disadvantages: Large files, may not be continuos spatially. All have further sttributes within.
Term
 Raster Data
Definition
 An image where each pixel is connected to a lat/long coordinate so it can be placed in relation to the real world. More continuous than vector data.
Term
 Attributes and Table
Definition
 The table of data associated with the GIS layer – points, lines and polygons.  Could be names, characteristics, area, rank, etc. associated with each part of a vector data set.
Term
 Joining External Data
Definition
 Combining attribute tables of two data sets to better analyze their info. Must have a primary key in common between the two. Example names or ID numbers same between both sets.
Term
 Field Calculator
Definition
 Used to create new information in an attribute table (new column) through calculations using information you already have. Example, area, proximity, etc.
Term
Definition
Term
 Analysis
Definition
 Individual Layer: Querying of individual data layers or across layers (e.g., “Selection”, select by attributes) Multiple Layer Analysis: • Overlays between data layers (select by location, clipping) Statistics: • Statistical Analysis (Using attributes to make statistical conclusions) Spatial Modeling: using multiple layers and various GIS functions in a process or sequence to get to an answer.
Term
 Four Approaches to GIS Data Input
Definition
 − Locating and downloading data layers off the web − Scanning a paper map, georeferencing it, online digitizing of features (points, lines, polygons) based on what you see − GPS data collection and mapping − Address or zipcode geocoding –> mapping using a table of addresses
Term
 Global Positioning System
Definition
 • GPS satellites broadcast information back to Earth – The time the message was broadcast – The orbital information of the satellite (satellite location) Need atleast three satellites to triangulate your location. 4 better for elevation. As many as possible is best.
Term
 Waypoints
Definition
 A location at which you have a marker on a GPS that you can navigate to or upload and use as data in GIS.
Term
 Common File Types
Definition
 .shp - A shape file, used for vector data. .jpeg/.tif - Image files used for raster data. .zip/.tar/.tgz/.exc - All types of compressed files. .gdb - A geodatabase file containing large amounts of data. .mxd - An ArcGIS map document.
Term
 Data Frame and their Use
Definition
 An element of the ArcMap user interface that displays a collection of layers drawn in a particular order for a specific map extent and map projection. Help us organize multiple layers of information within GIS.
Term
 “Projection on the Fly”
Definition
 An assumption GIS makes about the projection of a layer. Can cause problems when two layers have different projections.
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