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 

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.

• Ellipsoid/Spheroid

• Spherical or geographic coordinate system

• Datum

• Projection

• Units 

• 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

 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. 

 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.

1. 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.

• 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.

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.

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.

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.

 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.

− 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

• 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.

• .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.

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.