Lecture 3: Map Principles

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Questions and Answers

What do parallels represent in the coordinate system?

Fixed points of latitude only

A measure of distance between meridians

Circles around the Earth perpendicular to the north-south axis (correct)

Angles from the prime meridian

Which statement is true about meridians?

They divide the Earth into different hemispheres

They are circles that do not meet at the poles

All points on a meridian have the same latitude

They measure west-to-east angles from a reference meridian (correct)

What is the significance of the Equator in terms of parallels?

It is the only parallel that crosses meridians

It represents the origin of all meridians

It is the longest parallel and divides the Earth into two equal hemispheres (correct)

It has no geographical importance

How are solar times related to meridians?

Every point on a meridian shares the same solar or local time Signup and view all the answers

What does a graticule represent?

A grid of coordinate lines over the Earth's surface Signup and view all the answers

Why is the geographic north-south axis tilted at approximately 23.5°?

To account for different seasons and lengths of day and night Signup and view all the answers

What defines a point's location on Earth using the coordinate system?

Its latitude and longitude Signup and view all the answers

What does longitude measure?

Angles east or west from the prime meridian Signup and view all the answers

What is a primary characteristic of a geographic coordinate system?

It requires a spherical Earth model. Signup and view all the answers

Why do time-change boundaries rarely follow meridians?

To keep related places conveniently in the same time zone. Signup and view all the answers

Which of the following is a limitation of geographic coordinate systems?

They assume the Earth is spherical. Signup and view all the answers

What system uses a consistent Cartesian grid over a projection of the Earth's surface?

Rectangular coordinate system Signup and view all the answers

What defines the Prime Meridian?

It is fixed at 0º E/W at Greenwich. Signup and view all the answers

What is a drawback of using a rectangular coordinate system over large areas?

The grid lines vary in spacing drastically. Signup and view all the answers

Which information is NOT provided by a geographic coordinate system?

Consistent grid lines Signup and view all the answers

What is the purpose of the International Date Line?

To indicate regions experiencing daytime from those in night. Signup and view all the answers

What is the structure of the British National Grid reference?

2 letters followed by 3 figures(easting) and 3 figures(northing) Signup and view all the answers

What advantage does the Cartesian coordinate system provide in Geographic Information Systems?

It simplifies spatial computations such as distance and direction Signup and view all the answers

How many squares does each 500km square in the British National Grid get divided into?

25 Signup and view all the answers

What type of reference system does a postcode represent?

A hierarchical system Signup and view all the answers

Which of the following describes the nature of the British National Grid's 100km squares?

They omit the letter 'I' in their naming structure Signup and view all the answers

In the context of the Cartesian coordinate system, which of the following statements is true?

It allows location data to be given in metres. Signup and view all the answers

Which letters are used in the British National Grid reference for the 500km squares?

S, T, N, H, O Signup and view all the answers

What is the maximum number of figures in the full easting or northing reference in the British National Grid system?

6 Signup and view all the answers

Study Notes

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.

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Description

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.