1.1. Basic Terminology

Several useful terms are essential to discussing neogeography. Some are familiar, while others have specific contexts within a broader meaning. They are presented here for later referral as you progress through the book and are listed in a logical order so that terms build upon one another:

Coordinates

The geographic coordinates are the absolute position on the Earth (or any body). Typically these are Latitude and Longitude referenced to the WGS84 ellipsoid. Sometimes they will be referred to as "lat" and "lon." Latitude varies North-South, with 0 degrees at the Equator, varies from 90 to −90 degrees towards the poles, and is positive North. Longitude varies East-West, with 0 degrees at the Prime Meridian, varies from 180 to −180 degrees and is positive to East.

Coordinates can be represented in several formats:

• Decimal degrees (DD): 29.975

• Degrees-Minutes-Seconds (DMS): N29° 58' 30''

• Degrees-Minutes (DM): 29° 58.8'

The conversion is straightforward. There are 60 seconds in a minute, and 60 minutes in a degree.

Projection

A projection is required in order to display the three-dimensional Earth, which isn't a sphere but actually an oblate spheroid bulging in the center, onto any other shape. Typically, this is projection onto a two-dimensional map display, where Mercator and Rectangular (i.e., no transformation) projections are the most common. For example, Google Maps uses the Mercator Projection, which is good for zoomed-in viewing, but causes distortions when zoomed out. It is important to understand the implication of various projections depending on application and also when mixing together mapping providers.

POI (Points of Interest)

Points Of Interest, frequently abbreviated as POI, represents any significant locations such as public buildings, traveler's services, or user-defined waypoints. These may be categorized: restaurant, trail head, friend's house, scenic overlook, or scuba diving site. There is also AOI, Areas of Interest, which may include multiple POI or just a geographic area instead of a single point.

Extents

The bounding box, or farthest latitude and longitude of an AOI. This may also be referred to as just bbox. The extents define the Northern and Southern latitude, and the Easter and Western longitude. Extents are the simplest means of specifying the area of interest and are usually used for web service queries.

Tiles

Dynamic, or slippy maps, are composed of a set of individual square images. Each image is a tile. Together, these tiles are placed next to one another, or stitched, to give the impression of a large, sliding map.

Geolocation

The technique of automatically determining the position of something based on measured data. For example, it is possible to locate a computer given its IP address, or a mobile phone based on the observed cell towers. Geolocation is useful for determining where a user or device is without the user having to manually enter this information. GPS is a specific implementation of a geolocation technology.

GPS

GPS (Global Positioning System) really refers to the U.S. military owned and operated satellite network that provides three-dimensional location. GPS is also sometimes used to refer to any means of geolocation that provides geographic coordinates.

Simply put, GPS operates by a network of high-altitude space satellite broadcasting their position and time. Receivers use several of these observed broadcasts to determine its current position and time.

The European operated GPS system, Galileo, is currently expected to be operational by 2010 and will provide similar, but alternate, functionality to the current GPS.

Geotag

Adding location information to a document, photograph, audio sample, or some other type of data is an example of geotagging. Geotagging formats are not uniform and vary based on the type of document they modify. For example, a photograph can embed location information in the EXIF header of the file itself, or in many web applications the location information can be stored as triple-tags in the user specified tags.

Web Service

A web service is a resource that allows access to data or functionality from a provider—for example, a geocoder that takes an address and returns latitude and longitude is a web service, or a service to ask for all photos within 50 miles of a location. Web services typically use REST (Representational State Transfer) or SOAP (Simple Object Access Protocol) to allow programs and other sites to access the data.