Introduction to Reading Maps and Remote Sensing

Part 1 Reading Maps

Maps are likely the most widely used tool in geography. Maps are used to orient yourself to your surroundings, to identify characteristics of an area, and to protect or utilize resources. Maps often communicate far more than the written word, and the information within a map may have far reaching consequences. Few documents have more power to misinform than maps. Yet maps are regarded by most people simply as fact. It is important to look critically at maps. In some cases there may be problems with data collection. Was the sample size sufficient? Was the data randomly collected? Is there statistical significance? It is also important to question the intent of the map maker. Who drew the map? What was their objective? How has the data been classified? Should the data be classified? Is the map an appropriate scale? Which map projection was chosen and why? Is the level of detail on the map appropriate?

Other questions you might want to ask when consulting a map include: How recently was it printed? Could human error be a factor? What has been left off the map; and is that information significant?

Users of maps need to maintain a healthy skepticism. It is important to remember that a map is a collection of information subject to distortions arising from ignorance, greed, ideological blindness or malice.

An example of maps being misleading, is that in the early nineteenth century, popular notions of a Great American Desert in the central United States (confirmed on maps of the era), are considered to have slowed the pace of westward migration, until mid-century when the error was corrected.

Having said all of this, a well designed map helps to clearly identify problems or opportunities and can be used to create better solutions. A good map maker designs meaningful maps.

Sources of Maps and Air Photos

National Topographic System (NTS) maps are produced by the Surveys and Mapping Branch in Ottawa and are available from local suppliers. Alternatively, you can locate topographic maps and base maps online and create your own map.  Go to Toporama

Types of Maps

1. Thematic Map A thematic map (or chloropleth) map conveys information about specific characteristics of geographic features via different colors, line styles, hatch patterns, size of circles, frogs etc. These maps are composed of a geographic base map and a thematic overlay, and they depict information simply and clearly.
2. Mental Map A mental map is one which resides in our heads. These maps are rarely accurate in the traditional geometric way, but the images reveal our perceptions of the environment.
3. Reference Map The emphasis of a reference map is on location, and its purpose is to show a variety of features of the world or portion of it. A topographic map is a reference map which uses contour lines to show changes in relative relief. A planimetric map is a reference map which represents data such as location of roads and cities. There are basically two kinds of reference maps – ‘planimetric’ and ‘topographic’.
   • Planimetric MapsThese are the most common to the general public as road maps although there are numerous other features available on planimetric maps. They do not show topography (the elevation by means of contours). Soils, geological features, forest cover, political boundaries, socio-economic inventories, etc. are all forms of information that is available on planimetric maps.
   • Topographic Maps These maps show elevations with contour lines, lines joining points of equal elevation. The contour interval (the elevation difference between successive contour lines) may range from a low of one meter to hundreds of meters depending upon the scale of the map or the necessary requirement of projects.

Grid Systems for Precise Location

Some system is needed to identify where an object occurs on a map in relation to its location on the earths surface. Two systems are most common, ‘Latitude and Longitude’ and ‘UTM Grid’

Latitude and Longitude

• Latitude is a line drawn around the earth parallel to the equator. A series of these lines are drawn equidistant from each other and numbered from the equator to the north and south poles. A point can then be defined as so many degrees north or south of the equator to a maximum of 90 degrees.
• Longitude is a line drawn between the north and south poles. The first longitude is drawn through Greenwich, England and is called the Prime Meridian. Other longitudinal lines are drawn east and west of this Prime Meridian. Because of the shape of the earth these lines converge at the poles and have the widest separation at the equator. A point can be described as so many degrees (up to 180) east or west of the Prime Meridian.
• Using this system Castlegar would be located at 49⁰ 19′ N, 117⁰ 40′ W.

UTM Grid

• The UTM Grid system places a grid over sections of the Earth’s surface and describes location as a number of meters north of the equator and a number of meters east of the west-side (the false meridian) of the grid.  Because we commonly measure distance in meters in the field, this is an easier system for us to use than the latitude/longitude system.
• Using this system Castlegar would be located at UTM 11, 452500, 5460500N.  Earth is divided into 60 zones of 6 degrees each. We are in zone 11.Each grid is one million meters wide placed over the zone with the centre of grid at zone center. A false meridian (outside of the zone) is located at the left of the zone, and 500 000m E is at the center of zone. All measurements are taken East of false meridian and North of equator.

Map Surround

Each map has a margin around it containing important information to help you interpret items found on the map. Some of the information contained in the surround includes:

• Map Designation/Name
• Map Glossary
• True North – Magnetic Declination – Grid North
• UTM grid
• How this map relates spatially to others
• Copyright, conversions, scales, legend (also on back)

Scales and Manipulation The definition of scale is the ratio of ground distance (GD) to map distance (MD). Ground distance is always constant.

• Map Scales Within the map surround, you will find various types of scales to help you measure distances, areas, and the sizes of objects appearing on the map. You need to learn to convert between the various types since not all are included on every map sheet and some are more useful for some operations than others.
  • Representative Fraction (RF)   One unit on the map equals a number of units on the ground. Eq.   50000 or 1/50000 (hence the term fraction)  1 map unit = 50000 similar units on the ground. There are no identifiable units since any unit could be applied.  1 cm = 50000 cm or 1 inch = 50000 inches or 1 raisin = 50000 raisins

Part 2 Remote Sensing

Remote Sensing (RS) – acquiring information about an object or phenomenon, without making physical contact with the object. Eg. Looking at photographs, satellite imagery, aerial photographs, using drone or Google Earth etc.

Interpreting remotely sensing images is a skill that can only be developed with practice. It can be challenging because: images are often taken from an overhead perspective, which we normally don’t see; images may be taken using wavelengths outside of the visible portion of the spectrum; and the earth’s surface is shown at unfamiliar scales and resolutions.

Seven basic principles of Image interpretation It is important to remember that we often use a combination of these seven principles when interpreting imagery.

Relative Size E.g. houses relative to churches and schools; a mature tree from an immature tree; lake from pond, freeway from highway, cars from busses and trucks

Shape Shape can be recognized on a single photo or in stereo. E.g. Railroads – narrow with long curves and relatively level from roads which have sharper curves and steeper grades and mostly are wider.

Shadows Shadows often give valuable clues as the shape and relative size on an object, but they can also be a nuisance as they often obscure things. E.g. Shadows may indicate orientation of the photo if time of day is given. In the Northern hemisphere shadows are generally cast NE or NW.

Tone or Color Tone is only on black and white imagery. Tone varies from black to white with varying shades of gray in between Soil moisture content affects tone, darker = wetter; Gravel is the lightest;Water is the darkest unless it is reflecting light; Deciduous vs. Conifers reflect light differently – conifers area usually darker because of more shadow from lots of needles (and less reflectance).

Texture Texture ranges from smooth to coarse or rough E.g. Fine texture may denote a dense young stand of trees

Pattern The spatial arrangement of objects E.g. usually human influenced patterns tend toward well defined geometric patterns Tree Plantations vs. Natural regeneration; fire scars vs. harvesting patterns

Location (Site) and Association Sometimes individual features are hard to identify by themselves but when looked at in association with other features or objects their identity becomes more obvious.E.g. Cottonwood wouldn’t occur on dry ridges but rather in moist valley bottoms whereas, Ponderosa pine would be associated with dry ridges; or a dark smooth area in the middle of a wilderness is more likely to be a lake than a farmer’s field.