Maps and Models Dr. Miriam Helen Hill Behavioral Objectives

Maps and Models Dr. Miriam Helen Hill Behavioral Objectives The student will be able to: Define the vocabulary terms Identify latitude and longitude coordinates Identify map types Identify graph types Identify scale types by name Use a graphic scale Vocabulary Aerial photograph Globe Platform Attribute query GPS Political map Bar graph Graph Population pyramid Bi-lateral graph Graphic scale Prime Meridian Box-whisker chart Graticule Projection Bubble graph Greenwich Mean Time Proportional symbols Buffer Hachured contour Proportional symbol map Cadastral map High-low graph Query Cartogram Histogram Raster Cartographer Historical map Register Cartography History map Remote sensing Central meridian Isoline Remote sensing imagery Choropleth map Isoline interval Remote sensing platform Circle Isoline map Representative fraction Circle graph Large scale Resolution Climatograph Latitude RF Climograph Legend Sanborn map Cohort Line graph Satellite imagery Compromise Longitude Scale Conformal Loss-and-gain chart Scatter diagram Contour line Map Second DD Map reading Silhouette graph Degree Map interpretation Small scale Density Mercator Solar noon DMS Meridian Spatial query Dot density map Minute Stacked bar graph Equivalent Model Stereopair False color image Multiple-line graph Surface graph General reference map Overlay analysis Thematic map Geographic information science Parallel Thornthwaite diagram Geographic information studies Photogrammetry Topographic profile Geographic information system Pie chart Topographic quadrangle Geologic map Pixel Triangular graph Universal time Verbal scale Vector Wind rose Introduction Geographers use many tools to understand their subjects of study. Many people recognize that geographers are often cartographers or mapmakers. Cartography is the science of mapmaking, a very complex and exacting science. With the advent of computers, the facility to make maps and otherwise represent Earth has changed and expanded. The ways spatial patterns can be represented to enhance visualization and understanding rely on the foundations of cartography but are not limited to the pure conception of a map. This lesson will look at a variety of those tools and the basic knowledge needed to read and interpret graphic depictions of spatial data. A model is an idealized and generalized representation designed to depict the inherent properties, characteristics, and interactions of the subject. Models may be simple or complex and are often useful to explore the impact of changes or variations. Models may be descriptions of common characteristics, illustrations of similar properties or regions, computer simulations, numerical equations, solidly constructed objects, and conceptualizations. A globe is a spherical representation of Earth, an example of a model. The spherical shape demonstrates the shape of Earth. It is not exact, but it is close enough to depict important properties such as how latitude and longitude can be used to find points on Earth’s surface. A globe shows the axis as well as the two main features at the surface, land and water. Various globes may show political boundaries, landform patterns, and ocean currents. A movable circular bar may be attached to represent the circle of illumination. Although maps are a type of model, they are usually classified distinctly. Furthermore, holes can be found in most definitions. A map is generally a flat representation of locations on Earth’s surface. However, not all maps are flat, and neither must they be limited to the surface of Earth. They may not even be solid, because they may be in our minds or in computers. They generally depict locational elements or environmental characteristics in some manner. Map reading involves viewing a map and garnering information from it. Map interpretation involves using the data depicted on the map with other knowledge and data to draw inferences and conclusions. Map use skills, often, enable job performance and routine activities to be more efficient and effective. Another type of model is a graph. Graphs show numerical data in pictorial form. Like maps, they help clarify and summarize patterns and can be read and interpreted. Although the patterns may or may not be spatial, geographic data are often displayed on graphs. Latitude and Longitude One of the means by which locations on Earth are identified is by using latitude and longitude. Latitude measures north and south from the equator. Technically, the value is the angle formed between the line from the given point on Earth’s surface to Earth’s center and the line from there to the point on the equator nearest to the original location. Latitude is measured using east-west running lines called parallels, lines that are parallel to the equator. The latitude of the equator is 0°. The highest latitude possible is 90° or ¼ of the way around Earth (360° ÷ 4). Further around the earth means the angle measures less from the opposite side. All latitudes except the equator must be designated as either north or south. 90°N is the North Pole, and 90°S is the South Pole. With the exception of these two locations, a latitude alone defines a parallel of an infinite number of points. A degree (°) is divided into minutes and seconds. While a circle is 360°, a degree is 60 minutes (’), and a minute is 60 seconds (”). This is the same as time if an hour is substituted for a degree. Just as 30 minutes of time is half of an hour, 30 minutes of arc is half of a degree. Coordinates can be expressed in degrees, minutes, and seconds or DMS. They can, also, be converted to decimal degrees or DD, where the divisions of degrees are changed to decimals, such as tenths and hundredths of a degree. In order to locate an individual point, other than the poles, longitude must be provided following the latitude, geographically. Longitude measures east and west from the Prime Meridian that runs through an observatory in Greenwich near London, U.K. The north-south running lines used to measure longitude are meridians, and longitude is the angle measured east and west from the Prime Meridian or Greenwich Meridian. This starting location has a longitude of 0°. The highest longitude possible is half way around Earth or 180° (360° ÷ 2). Other than these two locations, all longitudes must be identified as either east or west of the Prime Meridian. See Figure 1. Longitude is the foundation of time. Earth turns on its axis once every 24 hours. With 360° in a circle, this means that Earth turns 15° in an hour. Solar noon is when the sun is over the meridian of a given location, so every longitude has a different time. To simplify matters, Earth has been generally divided into 24 time zones each differing by an hour. The central meridians have longitudes that are multiples of 15°, and these set the time for that zone. The time zone centered on the Prime Meridian sets Greenwich Mean Figure 1 Latitude and Longitude Time or Universal Time. Time zones to the east are later than times zones to the west, and the new day begins at the International Date Line at 180°. See Figure 2. Political conventions vary this model so that in reality, time zone boundaries are more complex and do not perfectly coincide with the longitude lines or have full hour differences. Figure 2 Central Meridians and 7.5° Boundaries (Politics Varies the Actual Time Zone Boundaries) Projections The spherical nature of Earth creates a major problem for cartographers. Consider trying to flatten an orange peel. It tears and breaks. Mathematical manipulations must be undertaken, then, to represent the spherical Earth’s surface in a flat form. These manipulations make projections. Three major categories of projections are equivalent, conformal, and compromise. An equivalent projection preserves the size of small areas on the map; and, thus, these can be used to compare areas or to explore density, number per area, relationships. Conformal projections maintain the shape of small areas. A map cannot be both equivalent and conformal! Another category of projections is the compromise projection, and these preserve neither area nor shape. Rather, compromise projections moderate and sacrifice both properties to make a nicer looking map. See Figure 3. Figure 3 Sample Projections Many map projections have been created. The Mercator projection is, perhaps, the most commonly recognized. Although it is made mathematically, the creation can be envisioned by considering a transparent globe marked with the latitude and longitude grid or graticule and the continents. A light bulb placed in the center would project these lines outward beyond the globe. If a rectangular piece of paper were to be wrapped around the globe touching or tangent around the equator, the continents and grid projected on to the surface of the paper would make a Mercator projection. Consider this projection. The parallels are parallel to each other, but they are not evenly spaced with higher latitudes. The meridians are, also, parallel rather than correctly converging toward the poles, and the poles cannot fall on the paper. An area at high latitude is much larger than an equal area near the equator, but the shapes of small areas are retained. Thus, this is a conformal projection. Greenland is a good location to observe to consider the properties of a projection. On the Mercator map, Greenland is huge compared to Saudi Arabia or Mexico, both of which are only a little smaller in area. If dots were placed on the map so one dot was in the center of each 10° area of the grid, the dots would be much more dispersed in Greenland than they would be near the equator. This Mercator projection cannot correctly show spatial distribution. Only projections that are equivalent projections are suited to this task. Scale Scale is another important consideration of maps and some models. Scale tells the size relationship between the map or model and the depicted part of Earth.

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