Global Positioning

Home

Tour

Physics

Chemistry

Earth Science

Environment

Scams

Lesson Plans

Introduction

Mapping

Local Geology

Regional Geology

Positioning

By: Lindsay Craig

Objective: You will also be able to plot latitude and longitude positioning grids and locate specific localities.

Reason: Latitude and longitude positioning grids are the most common positioning grids in use worldwide; everywhere on the Earth's surface can be defined by latitude and longitude.

A view from the top of Mount Davidson looking down on a portion of Virginia City in the lower left. Four of the five authors of this website are shown. The adjacent image shows the view from the top of Mt. Davidson looking down on a portion of Virginia City (lower left). Four of the five authors of this web site are shown. Imagine that you were at the top of Mt. Davidson hiking and taking in the spectacular view with your best friend and a thunderstorm rumbles in. Lightning bolts start cracking all around you, and your friend takes a bolt. You grab your cell phone and call for help. The dispatcher needs your position in order to send help. Instantly with a topographic map or a Global Positioning System (GPS) receiver you would be able to give the dispatcher exact and certain latitude and longitude coordinates; help's on the way. This is just one example of how positioning can be important. Global positioning helps people get jobs done, and some of these people are navigators and Virginia City surveyors. Who else uses positioning and maps?

People have created numerous systems for describing exact positions for anywhere on the Earth's surface. The United States Geological Survey (USGS) developed different topographic maps that utilize numerous useful positioning grids including Latitude and Longitude, Universal Transverse Mercator, Township and Range and Nevada Coordinate System (Nevada only). All of these are useful, but for our purpose only Latitude and Longitude will be discussed because it is the most widely used system of positioning worldwide. An apple sliced in half through the stem showing a western and eastern hemisphere

Slice an apple in half through its stem and you have created an east half and west half along a longitude cut. Put the apple back together and slice it in half perpendicular to the longitude cut. You have now created an equator or latitude line that separates the apple into north and south halves. With these two cuts have you created halves, quarters or thirds? By convention these sections are referred to as the NE, NW, SE and SW sections.

Longitude lines projected onto the Earth trace a straight line from the North Pole to South Pole. Longitude lines are based on degrees where there are 360 degrees to a full circle. There are 180 longitude lines on each half of the Earth. The zero degree longitude line is called the Prime Meridian and it was randomly chosen to pass through Greenwich, England. At this place you can put one foot on the east half of the Earth and one foot on the west half of the Earth. A sketch of a beet cut in slices from the root (south end) to the leaves (north end) showing that the smallest slices are at the ends

Latitude lines, on the other hand, measure from zero degrees at the equator and are evenly spaced both in the north and south hemisphere to 90 degrees at the poles. From the equator, each equally spaced slice gets smaller as the latitude lines get shorter. This is similar to the slicing of a beet as shown in the sketch to the right; the smallest slices are at the ends.

Sketch of the Earth showing the major continents and oceans with longitude and latitude lines Shown in the adjacent image are the major continents and oceans in a worldwide view displaying the relationship of longitude to latitude. In this sketching, the Earth's surface has been "peeled off a globe like an onion skin and pasted to a flat surface." Slices of longitude have been distorted into curves while lines of latitude remain as straight lines. Lines of latitude are greatest in length at the equator and progressively get shorter towards the poles. To keep the terms latitude and longitude straight it helps to remember that longitude lines are always "long" and latitude lines are always "lateral." Lateral means "sideways." On the sketching both longitude and latitude lines are drawn every 15 degrees. If this image were pasted back to the globe the longitude line on the right side would be the same line as the one on the left side.

Positioning

Home Tour Physics Chemistry Earth Science lEnvironment Scams Lesson Plans