GIS FINAL EXAM. Meridians Lines of equal longitude. Begin at 0 degrees, starting in Greenwich, England. Goes 180 degrees West and East;

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1 GIS FINAL EXAM Projecting GIS data & map projections Plannimetric coordinates - systems that are expressed in measures of x and y values. Geographic coordinates - systems, on the other hand, are expressed in values of longitude and latitude. Projection A process that involves conversion of data from Geographic Coordinates, Lat Long to projected coordinates. Reprojection Converts from one projected coordinate system to another (e.g., Michigan State plane to UTM). Meridians Lines of equal longitude. Begin at 0 degrees, starting in Greenwich, England. Goes 180 degrees West and East; Parallels Lines of equal latitude. The equator forms the 0 degrees and the poles are a 90 degrees. Measurements in N or S direction. Degrees-Minutes- Seconds (DMS) = Angular measures of location; One degree = 60 Minutes; One Minute = 60 Seconds; 46 33' 42" N, 87 24' 26" W = , " EARTH s SHAPE = A geoid (spheroid, ellipsoid) provides a precise model of this shape. The Earth is slightly flattened (due to centrifugal force and the Earth s rotation)

2 Datum - mathematical model of the Earth, serving as a reference for calculating geographic coordinates. initially derived using ground-based manual measurements (e.g., Clarke 1866) current models use satellite based measurements. If different datum are used to project the data a point can change in position from meters in communicated location! (e.g., NAD83 vs NAD27 vs. WGS84) MAP PROJECTIONS - the process of transforming a spherical (well technically a geodetic surface) surface onto a flat surface or plane (i.e., plannimetric surface). 3 Main Types of Projections; Conformal Preserves angles and shapes; Equidistant Preserves areas; Azimuthal Retains certain accurate directions (flat plane is fix to a single point on the earth usually a polar projection); Conformal Equidistant Azimuthal UTM - (Universal Trans-Mercator) Used for global purposes. US State plane system Used for individual states purposes. (Michigan State Plane Projected coordinate system) There are thousands of coordinate systems to use on GIS to suit your mapping area / purpose.

3 Commonly Used Projections Transverse Mercator - best known for mapping the world and is a conformal projection. Lambert Conformal Conic A conical projection used mainly for mapping East-West stretches at mid-latitudes due to it s conical shape and position minimizing distortion in these areas. Albers Equal Area Conical Similar to the Lambert except the Albers Equal Area projection, as the name suggests, offers an equal area projection as opposed to the Lambert system, which is conformal and preserves angles and shapes. Transverse Mercator Lambert Conformal Conic Albers Equal Area Conical Projection on the fly - a term that is used by the software companies. It implies data with different projection systems can be displayed simultaneously. Most of the time things work fine until your data arrive without a projection system. A default system is prescribed. This default system may not match what the data were mapped in originally and problems occur

4 Creating GIS Data & Digitizing Remotely sensed data - Satellite imagery: useful for land cover datasets; vegetation health, crop inventories, soil, geologic features and ocean or lake temperature data. - Higher resolution sensors: Quickbird and Ikonos helping provide precise datasets and map areas in detail. Field data GPS data, a familiar source for distances, elevations; Collected with hand/based surveys; GIS datasets are constantly updated using information collected using GPS equipment. Digitizing process of converting data from antilog to digital format.

5 Digitizing tables rarely used anymore, but they are a board with an electronic mesh that can sense the position of a cursor. A paper map is registered to the tablet and the mouse (cursor) traces the contents of the paper map to the digital environment; Scanning - is also a form of digitizing and converts an analog map to a scanned file. vectorization converting the raster lines into vector lines or areas for used in GIS vector datasets (shapefile, geodatabase etc.). heads up digitizing involves using a scanned image or a scanned document displayed on a computer monitor as a back-drop data source; Vector lines are traced over the image as a way of entering in the data. The GeoDatabase:Object based vector data model Coverages and Shapefiles are the forerunners to the latest development, the Geodatabase data model. Coverages 1980s (arrived with ArcInfo); Shapefiles 1990s (arrived with ArcView); Geodatabase 1999(ish) arrived with ArcGIS version 8 Geodatabases are the most sophisticated spatial data format of these three formats. GeoDatabases take advantage of object based technologies with a wider range of options as they are maintained and built by Database systems, Automatically maintains and updates topological relationships.

6 Points = 1 or more points; Polyline = set of line segments not always connected; Polygon = 1 or more rings or areas. Rings are closed connected lines. Feature class: Stores spatial data of the same geometric type; Feature dataset: stores feature classes that share the same coordinate system and extent. May contain different theme layers within the same file. Spatial features are represented as separate objects (e.g., a timber stand = one object) all the geometric shapes and attributes of the stand are stored in a single record; thus eliminating the need for the split file system. Enterprise GIS - This multi-user setting can become centralised database for an organisation and many users can access the information simultaneously, with various levels of accessibility. This multi-user centralized Database system is the fundamental concept of an Enterprise GIS. Versioning allows multiple users to edit the same data in an ArcSDE geodatabase (only) without applying locks or duplicating data. Archiving allows users to manage past changes sort of a temporal GIS.

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