Spatial Thinking

At no other time in the history of the world has it been easier to create or to acquire a map of nearly anything. Maps and mapping technology are literally and virtually everywhere. Though the modes and means of making and distributing maps have been revolutionized with recent advances in computing like the Internet, the art and science of map-making dates back centuries. This is because humans are inherently spatial organisms, and in order for us to live in the world, we must first somehow relate to it. Enter the mental map.

Mental Maps

Mental or cognitive maps are psychological tools that we all use every day. As the name suggests, mental maps are maps of our environment that are stored in our brains. We rely on our mental maps to get from one place to another, to plan our daily activities, or to understand and situate events that we hear about from our friends, family, or the news. Mental maps also reflect the amount and extent of geographic knowledge and spatial awareness that we possess.

Mental maps tend to have the following characteristics:

• Mental maps illustrate what we know about the places we live. They are rough “sketches” or ideas of our geographic knowledge of an area.
• Mental maps highlight how we relate to our local environment.
• What we choose to include and exclude on our map provides insights about what places we think are important and how we move through our places of residence.
• When we compare our mental maps to someone else’s from the same place, certain similarities emerge that shed light upon how we as humans tend to think spatially and organize geographical information in our minds.

To reinforce these points, consider the series of mental maps of Los Angeles provided below. Take a moment to look at each map and compare the maps with the following questions in mind:

• What similarities are there on each map?
• What are some of the differences?
• Which places or features are illustrated on the map?
• From what you know about Los Angeles, what is included or excluded on the maps?
• What assumptions are made in each map?
• At what scale is the map drawn?

Each map is probably an imperfect representation of one’s mental map. However, we can see some similarities and differences that provide insights into how people relate to Los Angeles, maps, and, more generally, the world. First, all maps are oriented so that north is up. Though only one of the maps contains a north arrow that explicitly informs viewers of the geographic orientation of the map, we are accustomed to most maps having north at the top of the page. Second, all but the first map identify some prominent features and landmarks in the Los Angeles area. For instance, Los Angeles International Airport (LAX) appears on two of these maps, as do the Santa Monica Mountains. How the airport is represented or portrayed on the map, for instance, as text, an abbreviation, or symbol, also speaks to our experience using and understanding maps. Third, two of the maps depict a portion of the freeway network in Los Angeles, and one also highlights the Los Angeles River and Ballona Creek. In a city where the “car is king,” how can any map omit the freeways?

What we include and omit on our mental maps, by choice or not, speaks volumes about our geographical knowledge and spatial awareness. Recognizing and identifying what we do not know is an essential part of learning. It is only when we identify the unknown that we can ask questions, collect information to answer those questions, develop knowledge through answers, and begin to understand the world where we live.

Asking Geographic Questions

Filling in the gaps in our mental maps and, more generally, the gaps in our geographic knowledge requires us to ask questions about the world where we live and how we relate to it. Such questions can be simple with a local focus (e.g., “Which way is the nearest hospital?”) or more complex with a more global perspective (e.g., “How is urbanization impacting biodiversity hotspots around the world?”). The thread that unifies such questions is geography. For instance, the question of “where?” is an essential part of the questions “Where is the nearest hospital?” and “Where are the biodiversity hotspots concerning cities?” Being able to articulate questions clearly and to break them into manageable pieces are valuable skills when using and applying a geographic information system (GIS).

Though there may be no such thing as a “dumb” question, some questions are indeed better than others. Learning how to ask the right question takes practice and is often more difficult than finding the answer itself. However, when we ask the right question, problems are more easily solved, and our understanding of the world is improved. There are five general types of geographic questions that we can ask and that GIS can help us to answer. Each type of question is listed here and is also followed by a few examples (Nyerges 1991). Nyerges, T. 1991. “Analytical Map Use.” Cartography and Geographic Information Systems (formerly The American Cartographer) 18: 11–22.

Questions about geographic location:

• Where is it?
• Why is it here or there?
• How much of it is here or there?

Questions about geographic distribution:

• Is it distributed locally or globally?
• Is it spatially clustered or dispersed?
• Where are the boundaries?

Questions about geographic association:

• What else is near it?
• What else occurs with it?
• What is absent in its presence?

Questions about geographic interaction:

• Is it linked to something else?
• What is the nature of this association?
• How much interaction occurs between the locations?

Questions about geographic change:

• Has it always been here?
• How has it changed over time and space?
• What causes its diffusion or contraction?

These and related geographic questions are frequently asked by people from various areas of expertise, industries, and professions. For instance, urban planners, traffic engineers, and demographers may be interested in understanding the commuting patterns between cities and suburbs (geographic interaction). Biologists and botanists may be curious about why one animal or plant species flourish in one place and not another (geographic location/distribution). Epidemiologists and public health officials are undoubtedly interested in where disease outbreaks occur and how, why, and where they spread (geographic change/interaction/location).

A geographic information system (GIS) can assist in answering all these questions and many more. Furthermore, GIS often opens up additional avenues of inquiry when searching for answers to geographic questions. Herein is one of the greatest strengths of the GIS. While GIS can be used to answer specific questions or to solve particular problems, it often unearths even more interesting questions. It presents more problems to be solved in the future.

Geographic Inquiry

Geography is the study of the physical and cultural environments of the earth. What makes geography different from other disciplines is that it is focusing on spatial inquiry and analysis. Geographers also try to look for connections between things such as patterns, movement and migration, trends, and so forth. This process is called a geographic or spatial inquiry.

In order to do this, geographers go through a geographic methodology that is quite similar to the scientific method, but again with a geographic or spatial emphasis. This method can be simplified in a six-step geographic inquiry process.

• Ask a geographic question. This means asking questions about spatial relationships in the world around you.
• Acquire geographic resources. Identify data and information that you need to answer your question.
• Explore geographic data. Turn the data into maps, tables, and graphs, and look for patterns and relationships.
• Analyze geographic information. Determine what the patterns and relationships mean concerning your question.

“Knowing where something is, how its location influences its characteristics, and how it influences relationships with other phenomena are the foundation of geographic thinking. This mode of the investigation asks you to see the world and all that is in it in spatial terms. Like other research methods, it also asks you to explore, analyze, and act upon the things you find. It also is important to recognize that this is the same method used by professionals around the world working to address social, economic, political, environmental, and a range of scientific issues” (ESRI).

Geographic Concepts

Before we can learn how to think geographically and apply spatial thinking, it is first necessary to review and reconsider a few key geographic concepts that are often taken for granted. For instance, what is a location, and how can it be defined? At what distance does a location become “nearby”? Or what do we mean when we say that someone has a “good sense of direction”? By answering these and related questions, we establish a framework that will help us to learn and to apply a GIS. This framework will also permit us to share and communicate geographic information with others, which can facilitate collaboration, problem-solving, and decision making.

Scale

When representing the Earth on a manageable-sized map, the actual size of the location is reduced. Scale is the ratio between the distance between two locations on a map and the corresponding distance on Earth’s surface. A 1:1000 scale map, for example, would mean that 1 meter on the map equals 1000 meters, or 1 kilometer, on Earth’s surface. Scale can sometimes be a confusing concept, so it is important to remember that it refers to a ratio. It does not refer to the size of the map itself, but rather, how zoomed in or out the map is. A 1:1 scale map of your room would be the same size of your room – plenty of room for significant detail, but hard to fit into a glove compartment.

As with map projections, the “best” scale for a map depends on what it is used for. If you are going on a walking tour of a historic town, a 1:5,000 scale map is commonly used. If you are a geography student looking at a map of the entire world, a 1:50,000,000 scale map would be appropriate. “Large” scale and “small” scale refer to the ratio, not to the size of the landmass on the map. 1 divided by 5,000 is 0.0002, which is a larger number than 1 divided by 50,000,000 (which is 0.00000002). Thus, a 1:5,000 scale map is considered “large” scale while 1:50,000,000 is considered “small” scale.

Location

The one concept that distinguishes geography from other fields is location, which is central to a GIS. Location is simply a position on the surface of the earth. What is more, nearly everything can be assigned a geographic location. Once we know the location of something, we can put it on a map, for example, with a GIS.

Generally, we tend to define and describe locations in nominal or absolute terms. In the case of the former, locations are simply defined and described by name. For example, city names such as New York, Tokyo, or London refer to nominal locations. Toponymy, or the study of place names and their respective history and meanings, is concerned with such nominal locations.

Though we tend to associate the notion of location with particular points on the surface of the earth, locations can also refer to geographic features (e.g., Rocky Mountains) or large areas (e.g., Siberia). The United States Board on Geographic Names maintains geographic naming standards and keeps track of such names through the Geographic Names Information Systems. The GNIS database also provides information about which state and county the feature is located as well as its geographic coordinates.

Contrasting nominal locations are absolute locations that use some type of reference system to define positions on the earth’s surface. For instance, defining a location on the surface of the earth using latitude and longitude is an example of absolute location. Postal codes and street addresses are other examples of absolute location that usually follow some form of local logic. Though there is no global standard when it comes to street addresses, we can determine the geographic coordinates (i.e., latitude and longitude) of particular street addresses, zip codes, place names, and other geographic data through a process called geocoding. There are several free online geocoders that return the latitude and longitude for various locations and addresses around the world.

With the advent of the global positioning system (GPS), determining the location of nearly any object on the surface of the earth is a relatively simple and straightforward exercise. GPS technology consists of a constellation of twenty-four satellites that are orbiting the earth and continuously transmitting time signals. To determine a position, earth-based GPS units (e.g., handheld devices, car navigation systems, mobile phones) receive the signals from at least three of these satellites and use this information to triangulate a location. All GPS units use the geographic coordinate system (GCS) to report location. Initially developed by the United States Department of Defense for military purposes, there is now a wide range of commercial and scientific uses of a GPS.

Location can also be defined in relative terms. Relative location refers to defining and describing places in relation to other known locations. For instance, Cairo, Egypt, is north of Johannesburg, South Africa; New Zealand is southeast of Australia; and Kabul, Afghanistan, is northwest of Lahore, Pakistan. Unlike nominal or absolute locations that define single points, relative locations provide a bit more information and situate one place in relation to another.

Direction

Like location, the concept of direction is central to geography and GIS. Direction refers to the position of something relative to something else, usually along a line. In order to determine direction, a reference point or benchmark from which direction will be measured needs to be established. One of the most common benchmarks used to determine direction is ourselves. Egocentric direction refers to when we use ourselves as a directional benchmark. Describing something as “to my left,” “behind me,” or “next to me” are examples of egocentric direction.

As the name suggests, landmark direction uses a known landmark or geographic feature as a benchmark to determine direction. Such landmarks may be a busy intersection of a city, a prominent point of interest like the Colosseum in Rome, or some other feature like a mountain range or river. The critical thing to remember about landmark direction, especially when providing directions, is that the landmark should be relatively well-known.

In geography and GIS, three more standard benchmarks are used to define the directions of true north, magnetic north, and grid north. True north is based on the point at which the axis of the earth’s rotation intersects the earth’s surface. In this respect, the North and South Poles serve as the geographic benchmarks for determining direction. Magnetic north (and south) refers to the point on the surface of the earth where the earth’s magnetic fields converge. This is also the point to which magnetic compasses point. Note that magnetic north falls somewhere in northern Canada and is not geographically coincident with true north or the North Pole. Grid north simply refers to the northward direction that the grid lines of latitude and longitude on a map, called a graticule, point to.

Distance

Complementing the concepts of location and direction is distance. Distance refers to the degree or amount of separation between locations and can be measured in nominal or absolute terms with various units. We can describe the distances between locations nominally as “large” or “small,” or we can describe two or more locations as “near” or “far apart.”

Calculating the distance between two locations on the surface of the earth can be quite involving because we are dealing with a three-dimensional object. Moving from the three-dimensional earth to two-dimensional maps on paper, computer screens, and mobile devices is not a trivial matter and is discussed in greater detail in a later chapter.

We also use a variety of units to measure distance. For instance, the distance between London and Singapore can be measured in miles, kilometers, flight time on a jumbo jet, or days on a cargo ship. Whether or not such distances make London and Singapore “near” or “far” from each other is a matter of opinion, experience, and patience. Hence the use of absolute distance metrics, such as that derived from the distance formula, provide a standardized method to measure how far away or how near locations are from each other.

Space

Where distance suggests a measurable quantity in terms of how far apart locations are situated, space is a more abstract concept that is more commonly described rather than measured. For example, space can be described as “empty,” “public,” or “private.”

Within the scope of a digital mapping or GIS, we are interested in space, and in particular, we are interested in what fills particular spaces and how and why things are distributed across space. In this sense, space is a somewhat ambiguous and generic term that is used to denote the general geographic area of interest.

One kind of space that is of particular relevance to a GIS is topological space. Simply put, topological space is concerned with the nature of relationships and the connectivity of locations within a given space. What is essential within topological space are (1) how locations are (or are not) related or connected, and (2) the rules that govern such geographic relationships.

Transportation maps such as those for subways provide some of the best illustrations of topological spaces. When using maps, we are primarily concerned with how to get from one stop to another along a transportation network. Specific rules also govern how we can travel along the network (e.g., transferring lines is possible only at a few key stops; we can travel only one direction on a particular line). Such maps may be of little use when traveling around a city by car or foot. However, they show the local transportation network and how locations are linked together effectively and efficiently.

Navigation

Transportation maps, like those discussed previously, illustrate how we move through the environments where we live, work, and play. This movement and, in particular, destination-oriented travel are generally referred to as navigation. How we navigate through space is a complex process that blends our various motor skills; technology, mental maps, and awareness of locations, distances, directions, and the space where we live. What is more, our geographical knowledge and spatial awareness are continuously updated and changed as we move from one location to another.

The acquisition of geographic knowledge is a lifelong endeavor. Though several factors influence the nature of such knowledge, we tend to rely on the three following types of geographic knowledge when navigating through space:

• Landmark knowledge refers to our ability to locate and identify unique points, patterns, or features (e.g., landmarks) in space.
• Route knowledge permits us to connect and travel between landmarks by moving through space.
• Survey knowledge enables us to understand where landmarks are concerning each other and to take shortcuts.

Each type of geographic knowledge is acquired in stages, one after the other. For instance, when we find ourselves in a new or unfamiliar location, we usually identify a few unique points of interest (e.g., hotel, building, fountain) to orient ourselves. We are, in essence, building up our landmark knowledge. Using and traveling between these landmarks develops our route knowledge and reinforces our landmark knowledge and our overall geographical awareness. Survey knowledge develops once we begin to understand how routes connect landmarks and how various locations are situated in space. It is at this point, when we are somewhat comfortable with our survey knowledge, that we can take shortcuts from one location to another. Though there is no guarantee that a shortcut will be successful, if we get lost, we are at least expanding our local geographic knowledge.

Landmark, route, and survey knowledge are the cornerstones of having a sense of direction and frame our geographical learning and awareness. While some would argue that they are born with a good sense of direction, others admit to always getting lost. The popularity of personal navigation devices and online mapping services speaks to the overwhelming desire to know and to situate where we are in the world. Though developing and maintaining a keen sense of direction presumably matters less and less as such devices and services continue to develop and spread, it can also be argued that the more we know about where we are in the world, the more we will want to learn about it.

This section covers concepts essential to geography, GIS, and many other fields of interest. Understanding how location, direction, and distance can be defined and described provides an essential foundation for the successful use and implementation of a GIS. Thinking about space and how we navigate through, it also serves to improve and own geographic knowledge and spatial awareness.

Understanding Maps

A map can be defined as a graphic representation of the real world. Because of the infinite nature of our Universe, it is impossible to capture all of the complexity found in the real world. For example, topographic maps abstract the three-dimensional real world at a reduced scale on a two-dimensional plane of paper. Cartography is the art and science of making maps, and a cartographer is professional who creates maps.

Maps are among the most compelling forms of information for several reasons. Maps are artistic. Maps are scientific. Maps preserve history. Maps clarify. Maps reveal the invisible. Maps inform the future. Regardless of the reason, maps capture the imagination of people around the world. As one of the most trusted forms of information, map makers, and geographic information system (GIS) practitioners hold a considerable amount of power and influence. Therefore, understanding and appreciating maps and how maps convey information are essential aspects of GIS. The appreciation of maps begins with exploring various map types.

So what exactly is a map? Like GIS, there are probably just as many definitions of maps as there are people who use and make them. We can define a map simply as a representation of the world. Such maps can be stored in our brain (i.e., mental maps), they can be printed on paper, or they can appear online. Notwithstanding the actual medium of the map (e.g., our fleeting thoughts, paper, or digital display), maps represent and describe various aspects of the world. For purposes of clarity, the three types of maps are the reference map, the thematic map, and the dynamic map.

Most maps allow us to specify the location of points on the Earth’s surface using a coordinate system. For a two-dimensional map, this coordinate system can use simple geometric relationships between the perpendicular axes on a grid system to define spatial location. Two types of coordinate systems are currently in general use in geography: the geographical coordinate system and the rectangular (also called Cartesian) coordinate system.

Geographic Information Science (GIScience)

Reference Maps

The primary purpose of a reference map is to deliver location information to the map user. Geographic features and map elements on a reference map tend to be treated and represented equally. In other words, no single aspect of a reference map takes precedence over any other aspect. Moreover, reference maps generally represent geographic reality accurately. Examples of some common types of reference maps include topographic maps such as those created by the United States Geological Survey (USGS) and image maps obtained from satellites or aircraft that are available through online mapping services.

The accuracy of a given reference map is indeed critical to many users. For instance, local governments need accurate reference maps for land use, zoning, and tax purposes. National governments need accurate reference maps for political, infrastructure, and military purposes. People who depend on navigation devices like global positioning systems (GPS) units also need accurate, and up-to-date reference maps to arrive at their desired destinations.

Thematic Maps

Contrasting the reference map are thematic maps. As the name suggests, thematic maps are concerned with a particular theme or topic of interest. While reference maps emphasize the location of geographic features, thematic maps are more concerned with how things are distributed across space. Such things are often abstract concepts such as life expectancy around the world, per capita gross domestic product (GDP) in Europe, or literacy rates across India. One of the strengths of mapping, and in particular of thematic mapping, is that it can make such abstract and invisible concepts visible and comparable on a map.

It is important to note that reference and thematic maps are not mutually exclusive. In other words, thematic maps often contain and combine geographical reference information, and conversely, reference maps may contain thematic information. What is more, when used in conjunction, thematic and reference maps often complement each other.

For example, public health officials in a city may be interested in providing equal access to emergency rooms to the city’s residents. Insights into this and related questions can be obtained through visual comparisons of a reference map that shows the locations of emergency rooms across the city to thematic maps of various segments of the population (e.g., households below poverty, percent elderly, underrepresented groups).

Thematic maps are generally are more abstract, involving more processing and interpretation of data, and often depict concepts that are not directly visible; examples include maps of income, health, climate, or ecological diversity. There is no clear-cut line between reference and thematic maps, but the categories are useful to recognize because they relate directly to how the maps are intended to be used and to decisions that their cartographers have made in the process of shrinking and abstracting aspects of the world to generate the map. Different types of thematic maps include:

• choropleth – a thematic map that uses tones or colors to represent spatial data as average values per unit area
• proportional symbol – uses symbols of different sizes to represent data associated with different areas or locations within the map
• isopleth– also known as contour maps or isopleth maps depict smooth continuous phenomena such as precipitation or elevation
• dot density – uses a dot symbol to show the presence of a feature or phenomenon – dot maps rely on a visual scatter to show a spatial pattern
• dasymetric – an alternative to a choropleth map but instead of mapping the data so that the region appears uniform, ancillary information is used to model the internal distribution of the data

Within the context of a GIS, we can overlay the reference map of emergency rooms directly on top of the population maps to see whether or not access is uniform across neighborhood types. There are other factors to consider when looking at emergency room access (e.g., access to transport), but through such map overlays, underserved neighborhoods can be identified.

When presented in hardcopy format, both reference and thematic maps are static or fixed representations of reality. Such permanence on the page suggests that geography and the things that we map are also in many ways, fixed or constant. This is far from reality. The integration of GIS with other forms of information technology like the Internet and mobile telecommunications is rapidly changing this view of maps and mapping, as well as geography at large.

Dynamic Maps

The diffusion of GIS and the popularity of online mapping tools and applications speak to this shift in thinking about maps and map use. In this regard, it is worthwhile to discuss the diffusion of dynamic maps. Dynamic maps are simply changeable or interactive representations of the earth. Dynamic mapping refers more to how maps are used and delivered to the map user today (e.g., online, via mobile phone) than to the content of the map itself. Both reference and thematic maps can be dynamic, and such maps are an integral component of any GIS. The critical point about dynamic maps is that more and more people, not just GIS professionals, have access to such maps.

Unlike a hardcopy map that has features and elements, users cannot modify or change, dynamic maps encourage and sometimes require user interaction. Such interaction can include changing the scale or visible area by zooming in or zooming out, selecting which features or layers to include or to remove from a map (e.g., roads, imagery), or even starting and stopping a map animation.

Just as dynamic maps will continue to evolve and require more user interaction in the future, map users will demand more interactive map features and controls. As this democratization of maps and mapping continues, the geographic awareness and map appreciation of map users will also increase. Therefore, it is of critical importance to understand the nature, form, and content of maps to support the changing needs, demands, and expectations of map users in the future.

Topographic Maps

Maps are used to display both the cultural and physical features of the environment. Standard topographic maps show a variety of information including roads, land-use classification, elevation, rivers and other water bodies, political boundaries, and the identification of houses and other types of buildings. Some maps are created with particular goals in mind, with an intended purpose.

Most maps allow us to specify the location of points on the Earth’s surface using a coordinate system. For a two-dimensional map, this coordinate system can use simple geometric relationships between the perpendicular axes on a grid system to define spatial location. Two types of coordinate systems are currently in general use in geography: the geographical coordinate system and the rectangular (also called Cartesian) coordinate system.

Have you ever found driving directions and maps online, used a smartphone to ‘check-in’ to your favorite restaurant, or entered a town name or zip code to retrieve the local weather forecast? Every time you and millions of other users perform these tasks, you are making use of Geographic Information Science (GIScience) and related spatial technologies. Many of these technologies, such as Global Positioning Systems (GPS) and in-vehicle navigation units, are very well-known, and you can probably recall the last time you have used them.

Geographic Information Science (GIScience)

Other applications and services that are the products of GIScience are a little less obvious, but they are every bit as common. If you are connected to the Internet, you are making use of geospatial technologies right now. Every time your browser requests a web page from a Content Delivery Network (CDN), a geographic lookup occurs and the server you are connected to contacts other servers that are closest to it and retrieves the information. This happens so that the delay between your request to view the data and the data being sent to you is as short as possible.

GIScience and the related technologies are everywhere, and we use them every day. When it comes to information, “spatial is special.” Reliance on spatial attributes is what separates geographic information from other types of information. There are several distinguishing properties of geographic information. Understanding them, and their implications for the practice of geographic information science is a key utilizing geographic data.

• Geographic data represent spatial locations and non-spatial attributes measured at certain times.
• Geographic space is continuous.
• Geographic space is nearly spherical.
• Geographic data tend to be spatially dependent.

Spatial attributes tell us where things are, or where things were at the time the data were collected. By merely including spatial attributes, geographic data allow us to ask a plethora of geographic questions. For example, we might ask, “are gas prices in Puyallup high?” The interactive map from GasBuddy.com can help us with such a question while enabling us to generate many other spatial inquiries related to the geographic variation in fuel prices.

Another essential characteristic of geographic space is that it is “continuous.” Although the Earth has valleys, canyons, caves, oceans, and more, there are no places on Earth without a location, and connections exist from one place to another. Outside of science fiction, there are no tears in the fabric of space-time. Modern technology can measure location very precisely, making it possible to generate incredibly detailed depictions of geographic feature location (e.g., of the coastline of the eastern U.S). It is often possible to measure so precisely that we collect more location data than we can store and much more than is useful for practical applications. How much information is useful to store or to display in a map will depend on the map scale (how much of the world we represent within a fixed display such as the size of your computer screen) as well as on the map’s purpose. The map below is a digital elevation model (DEM), that is considered continuous because elevation always exits on the planet.

In addition to being continuous, geographic data also tend to be spatially dependent. More simply, “everything is related to everything else, but near things are more related than distant things” (which leads to an expectation that things that are near to one another tend to be more alike than things that are far apart). How alike things are in relation to their proximity to other things can be measured by a statistical calculation known as spatial autocorrelation. Without this fundamental property, geographic information science as we know it today would not be possible.

Geographic data comes in many types, from many different sources and captured using many techniques; they are collected, sold, and distributed by a wide array of public and private entities. In general, we can divide the collection of geographic data into two main types:

• Directly collected data
• Remotely sensed data

Directly collected data are generated at the source of the phenomena being measured. Examples of directly collected data include measurements such as temperature readings at specific weather stations, elevations recorded by visiting the location of interest, or the position of a grizzly bear equipped with a GPS-enabled collar. Also, included here are data derived from surveys (e.g., the census) or observation (e.g., Audubon Christmas bird count).

Remotely sensed data are measured from remote distances without any direct contact with the phenomena or need to visit the locations of interest. Satellite images, sonar readings, and radar are all forms of remotely sensed data.

Maps are both the raw material and the product of geographic information systems (GIS). All maps represent features and characteristics of locations, and that representation depends upon data relevant at a particular time. All maps are also selective; they do not show us everything about the place depicted; they show only the particular features and characteristics that their maker decided to include. Maps are often categorized into reference or thematic maps based upon the producer’s decision about what to include and the expectations about how the map will be used. The prototypical reference map depicts the location of “things” that are usually visible in the world; examples include road maps and topographic maps depicting terrain.