Lecture 3: Map Principles

Introduction to GIS - Map Principles

• GIS stands for Geographic Information Systems
• Map principles are fundamental to GIS
• Coordinate systems are used to locate points on a map
• Parallels and meridians form a grid on the Earth's surface
• Latitude measures angles north or south of the equator
• Longitude measures angles east or west of the prime meridian
• The Earth is a three-dimensional object that appears spherical
• The Earth's surface has a constant radius
• Any point on Earth can be uniquely identified using latitude and longitude coordinates

Presentation Outline

• Coordinate systems
• Parallels and meridians
• Spatial referencing
• Rectangular coordinate systems
• Non-coordinate systems

Coordinate Systems

• The Earth is a sphere
• Latitude and longitude are used to identify points
• Latitude measures north-south angles from a reference parallel (equator)
• Longitude measures west-east angles from a reference meridian (typically Greenwich)
• Latitude and longitude are measured in degrees

Origins of Latitude and Longitude

• Latitude (φ) and longitude (λ) coordinates are angles measured from the Earth's center to any point on the earth's surface
• One arrow lies over the north-south geographical axis and the other in the east–west direction
• These arrows define the origin of the coordinate system's
• Every point on the planet's surface can be located using these coordinates

Longitude and Latitude - 3D Schematic

• Latitude is represented by the angle A degrees North
• Longitude is represented by the angle B degrees West

Longitude and Latitude in 2D

• Shows the relationship between longitude and latitude lines
• Longitude lines are vertical and perpendicular to latitude lines
• Latitude lines are horizontal and parallel to each other
• Longitude ranges from -180° to 180°
• Latitude ranges from -90° to 90°

Parallels and Meridians

• A graticule is a spherical grid of coordinate lines
• Parallels are circles perpendicular to the north-south axis
• Meridians are semicircular arcs with the axis as chord
• Parallels do not intersect
• All meridians meet at the poles
• Parallels intersect meridians at 90-degree angles

Properties of Parallels

• Parallels are natural references
• The longest parallel is the Equator
• The Equator divides the Earth into the Northern and Southern Hemispheres
• The Earth's tilted axis, about 23.5 degrees, affects the seasons and day/night lengths.

Properties of Meridians

• All points on a meridian share the same local time
• The world is divided into 24 time zones, each 15° wide.
• Time zones do not always follow meridians exactly but adjust for political and societal reasons.
• The prime meridian is located at Greenwich, England and is the 0° degree line.
• The international date line is opposite the prime meridian

Spatial Referencing

• A system used to locate features on the Earth's surface, or a 2D representation
• The system should be consistent and stable
• It should show points, lines, and polygons
• It should allow the measurement of length, area, and shape
• GIS uses various systems of spatial referencing.

Geographic Coordinate Systems

• Assumes the Earth is spherical
• Constructed using lines of latitude (north-south) and longitude (east-west)
• Equator is at 0° latitude
• Greenwich Meridian is at 0° longitude

Issues of Geographic Spatial Referencing

• Assumes the Earth is a perfect sphere
• Distances between latitude and longitude lines change depending on location
• Lines on projected maps are distorted leading to inaccuracies in precision
• Projections distort longitude and latitude measurements

Rectangular Coordinate Systems (Cartesian Grid)

• A regular, Cartesian grid is laid over a projection of the Earth's surface
• Coordinate system using X and Y axes
• Lines of Lat/Long are irregular, rectangular coordinates are not
• Systems are only applied to small areas.

British National Grid (Cartesian Grid)

• Used for Great Britain
• Ordnance Survey map references (2 letters, 3 numbers, 3 numbers) to locate areas on the map.
• Grid squares and coordinates help precisely identify locations across the British Isles

Advantages of Rectangular Coordinates

• Spatial computations (distance, directions) are easy
• Location data is in meters
• X and Y coordinates match computer screens

Non-Coordinate Systems

• Provide spatial reference using coded systems (e.g., postcodes)
• Codes can be translated into coordinates
• In the UK, the most common non-coordinate system is postcode

Non-Coordinate Systems - Postcodes

• Postcodes in the UK are hierarchical, with increasing specificity of address
• Regions, districts, sectors, and units
• Postcodes are useful for identifying defined areas but not points on a map
• Convert to coordinates/centroids is often needed to work within other GIS layers

Spatial Referencing - Summary

• Numerous methods for referencing space exist
• Geographic systems for global coverage
• Rectangular for localized coverage
• Non-coordinate systems for entities, but need more info to use in other systems.

This quiz explores the fundamental concepts of geographic coordinate systems, including the significance of parallels and meridians, the implications of the Equator, and the Prime Meridian. Test your knowledge on how coordinates define locations and time zones on Earth.