Introduction to GIS - Map Principles

Introduction to GIS - Map Principles

• GIS stands for Geographical Information Systems
• The presentation outlines map principles, including coordinate systems, parallels and meridians and spatial referencing methods.
• Earth is a three-dimensional object, approximating a sphere
• A point on Earth's surface is uniquely identified using latitude and longitude.
• Latitude measures angles north or south from the equator.
• Longitude measures angles east or west from a reference meridian.
• The Greenwich Meridian is the 0° longitude line, often identified as the prime meridian.
• The international date line is 180° from the prime meridian.

Presentation Outline

• Coordinate systems
• Parallels and meridians, spatial referencing
• Rectangular coordinate systems
• Non-coordinate systems

Coordinate Systems

• Latitude and longitude define a point on Earth.
• Latitude is measured in degrees north or south of the equator.
• Longitude is measured in degrees east or west of the Greenwich Meridian.
• Latitude and longitude define a point's position based on its intersection with a parallel and a meridian.

Origins of Latitude and Longitude

• The north-south axis corresponds to the Earth's axis.
• The east-west axis is perpendicular to the north-south axis.
• Any location can be identified with the two angles: longitude (λ) and latitude (φ).

Longitude and Latitude: 3D Schematic

• The Earth is divided by lines of latitude and longitude
• Latitude lines run parallel to the equator.
• Longitude lines run through the north and south poles
• The prime meridian is 0 degrees longitude.
• Positions are specified by degrees N or S of the equator and degrees W or E of the prime meridian.

Longitude and Latitude in 2D

• Latitude lines are parallel to the equator.
• Longitude lines converge at the poles.
• Latitude and longitude measure angles based on Earth's spherical shape
• The Prime Meridian is located at 0 degrees longitude.

Parallels and Meridians

• A graticule is the grid of lines of Latitude and Longitude.
• Parallels, lines of latitude, are parallel to the Equator.
• Meridians, lines of longitude, pass through the north and south poles.
• All meridians meet at the poles.
• Parallels do not cross each other.
• Parallels are used as a reference.
• Parallels are tilted relative to the Earth's orbital plane, which causes the seasons.

Properties of Parallels

• The equator is the longest parallel, dividing Earth into the northern and southern hemispheres.
• The Earth's north-south axis is tilted relative to its orbital plane creating the seasons.

Properties of Meridians

• All points on a meridian share the same solar/local time.
• The Earth is divided into 24 time zones (each 15° wide).
• Time zone boundaries often deviate from meridians to accommodate national/regional boundaries.
• The prime meridian is located in Greenwich, near London.
• The opposite prime meridian is the international date line.

Spatial Referencing

• A system for locating features on Earth or its 2D representations.
• The system should be consistent and stable, able to show points, lines and polygons, allowing length, area, and shape measurement.
• GIS uses three types: geographic coordinate systems, rectangular coordinate systems, and non-coordinate systems.

Geographic Coordinate Systems

• Assumes the Earth is spherical.
• Divides the Earth into latitude and longitude lines (north-south and east-west).
• The equator is at 0° latitude.
• The Greenwich Meridian is at 0° longitude.
• Angular measurements from the Earth's center specify locations.

Issues of Geographic Spatial Referencing

• Assumes the Earth is spherical
• Distances between latitude and longitude lines decrease at the poles, increasing precision issues.
• Lines of latitude and longitude, when projected onto a map, become distorted.

Rectangular Coordinate Systems (Cartesian Grid)

• A regular grid system over a map projection of the Earth.
• Grid lines are consistent across the map.
• Useful in smaller areas with consistent grid spacing reflecting geographic space. - Different from Latitude/Longitude
• Examples such as the British National Grid.

British National Grid

• Ordnance Survey map reference system for Great Britain.
• Uses letters and numbers to reference coordinates.
• The reference consists of 2 letters, 3 numbers, followed by 3 numbers (e.g., NA123456)
• Based on a 500km square grid system, subdivided into 25 sections.
• Each square is further divided into 100km squares, each associated with a letter (A-Z excluding I).

Advantages of Rectangular Coordinates

• Ease of spatial computations (distance, direction)
• Data in meters, aligning with computer screen coordinates
• Useful in GIS software

Non Coordinate Systems

• Provide spatial reference using descriptive codes.
• Examples: Postcodes
• Postcodes can be translated to coordinate systems
• In the UK, postcodes are widely used.

Non-coordinate Systems - Postcodes

• Postcodes are hierarchical (region, district, sector, etc.)
• Postcodes pinpoint locations within increasingly small areas (not points)
• Useful for objects associated with a given postcode but not for point analysis.
• Converting postcodes to centroid points is often necessary for certain analyses.

Spatial Referencing - Summary

• Various methods exist for referencing locations (space).
• Geographic systems provide global coverage.
• Rectangular coordinates are suited for smaller areas (like national grids).
• Non-coordinate systems (e.g., postcodes) are suitable for specific use-cases.

This quiz covers the fundamental principles of map-making within Geographic Information Systems (GIS). Learn about coordinate systems, parallels, meridians, and spatial referencing to better understand how to accurately identify locations on Earth. Enhance your knowledge on how latitude and longitude work together to define points on the three-dimensional globe.