GPS and Mapping

An introduction

by Nigel Hanlon - Software Developer


Who am I?

Senior Software Developer at Openapp

Work primarily on GIS.

(I develop maps to solve problems)

.. and of course, Cassie's husband.

About this Talk

Mapping and Coordinate Systems

Introduction to GPS

Search and Rescue Technology

Questions and Answers

Mapping and Coordinate Systems

What is a map?

A visual representation of an area showing features such as cities, rivers, roads or mountains.


What makes a map different from a picture?



All Maps have a scale.

A Scale tells us distance.

Scales are expressed as ratios.

A 1:100000 scale map means that 1cm on the map is worth one 1km on the ground.

All maps have Coordinates

Coordinates tell us where (location)

They allow us to represent a location accurately.

Go down the road here about a mile and when you see a green gate it's the third house on the right.


It's at 53.550° N, 7.33° W

A location is a set of Coordinates

There are many different ways to write the same coordinates.

One method you may be familiar with is a National Grid.

Irish National Grid

The Problem with Grids

The world is round.

Maps are square.

Latitude and Longitude

Latitude and Longitude

How many of these look familiar?

N 444 557 - OSI Grid Reference

244464 E, 255704 N - Irish National Grid

644406 E, 755726 N - Irish Transverse Mercator

53.550° N, 7.33° W - WGS84 (Decimal Lat/Lon)

53° 32' 58.5"N, 07° 19' 47.7"W - WGS84 (Deg, Min, Sec)

53° 32.9747' N, 7° 19.795' W - WGS84 (Deg, Decimal Min)

Where was it?

Introduction to GPS

The basics

Stands for Global Positioning System

Consists of a network of satellites in orbit.

Allows anyone with a GPS receiver to find their location.

What is it used for?

Navigation for People/Cars/Boats/Aircraft etc

Surveying, Mapping and Construction

Security and Cargo

Mobile Phone networks

Financial Services

Search and Rescue


US began the GPS project in 1973 to replace older systems.

Navstar (Navigation System Using Timing and Ranging)

Korean Air Lines Flight 007 was shot down in 1983 after straying into the USSR.

Ronald Reagan issued a directive making GPS freely available for civilian use.

Fully Operational in April 1995

NAVSTAR constellation

24 satellites in orbit, at least 4 in view regardless of location.

Each equipped with a very accurate atomic clock.

Broadcasts current time and position.

GPS Alternatives

GLONASS - Russian GLObal NAvigation Satellite System

IRNSS - Indian Regional Navigation Satellite System

COMPASS/BeiDou - Chinese Navigation Satellite System

Galileo/GNSS - European Union (Active in 2020)

So how does it work?

Distance, Speed and Time

You are driving home at 100km/hr

Home is two hours away.

Assuming your speed is constant, how far do you have to travel in km?

The answer?


distance = speed x time

distance = 100km/hr x 2 hours

200km = 100km/hr x 2 hours

Factors Affecting GPS Accuracy

Weather conditions and line of sight

Number of Satellites in view

Local interference

Previous usage

Time travel

Search and Rescue Technology


Questions and Answers