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The Nature of Geographic Inquiry

The nature of spatial analysis
The nature of spatial analysis
Danny M. Vaughn, Ph.D., CMS

Geographic inquiry follows a similar structured path as the scientific method in that it begins with asking geographic (spatially focused) questions, followed by acquiring, organizing, and analyzing geographic information; and ultimately coming up with defensible answers to the questions. A good investigation should also spawn new questions that will serve to identify additional work for future projects.

Any analysis follows one or more of the following questions: Who (person)? What (result, inventory, or object)? Where (location)? When (time)? How (process or action)? Why (explanation)? Combinations of these basic questions are generally built in a spatial query. Some example questions include:

What species of trees (object) are growing on the north side (where) of Mt. St. Helens?

What (inventory) are the classes of volcanic deposits, and where are they distributed throughout the blast zone?

What areas (object/location) of the blast zone have changed in terms of vegetation density (biomass)?

What (result) will be the overall distribution (spatial patterns) of vegetation over the next 20 years (when) on the north face of Mt. St. Helens?

When will the blast zone be stabilized from mass movements?

Why (an explanation) are there very few vegetation types on the Sasquatch Staircase (north face)?

How will seasonal weather conditions affect mass movements on the north slopes?

How (process) does precipitation and temperature impact slope stability (what) on southeast, south, and southwest aspect slopes (where) in each of the four seasons (when)?

When a mass movement occurs in a valley (what, object), how will it affect the streams course (where)?

What if …? These are spatial modeling questions that take on a more sophisticated research direction. They imply future prediction based upon any number of identified criteria.

Spatial Associations

The geographic information system (GIS) enables an investigator to display and analyze spatial associations of geographic elements representing “real world” objects. Geographic location and position are probably the most obvious, although there are a number of comparative associations that can be addressed. While the question where is addressed with regard to location, objects can also be described within an area or region by their pattern, density, and clustering. Pattern suggests something is influencing the spatial distribution, although a lack of pattern can also be significant in that it may suggest an anomaly that is not a function of a normal condition or process. Trees aligned in a linear pattern may suggest the underlying geology has some control or influence. On the other hand, specific vegetation species that are not indigenous to an area may suggest something more interesting is a contributing factor. Density refers to the number of objects taking up an area or region, which may be an indication of health, vigor, soil chemistry, presence of pollutants, etc. When objects are in highly concentrated areas, it suggests they are grouped for some explainable reason. Clustering will generally indicate something is controlling the manner in which objects have assembled. In each of these examples, their spatial association can be determined by asking and investigating the questions how and why.

There are many more ways a GIS can evaluate spatial associations. The regional concept is clearly geographic. Its focus is on how humans affect the environment, and how the environment affects humans. Geographers seek to establish linkages or connectivity among the human and physical elements that collectively define a region. Through the application of a GIS an investigator can examine a number of conditions that might prompt an entire society of people to relocate (spatial transition). Radical changes in climate and topography would certainly qualify as an impetus resulting in significant evolutionary changes in dress, food source, food type, shelter, religious beliefs, and culture. Maps can be developed to illustrate a relationship between changes in physical processes (climate, volcanic and earthquake activity, flooding, etc,), migration patterns that track the movement of people, and their ultimate relocation. Unraveling the many complex factors in the human and physical dimensions of the world become more clearly understandable when illustrated in time series or time change analysis. The ability to separate layers of thematic content, selectively define only the appropriate conditions, and create specific spatial relationships is one of many powerful tools of the GIS.

Analytical Operations

Retrieval functions include selective search, manipulation, and output of data without modifying the geographic location of features, or creating new spatial objects.

Classification includes identifying a set of features as belonging to a group, defining patterns and associations, recoding objects by number, and assigning a class name (e.g. land use). Classification is used to generalize or assign identities to features. Classification is controlled segregation.

Measurement functions include establishing distances between points, lengths of lines, perimeters, areas, volumes, etc.

Overlay operations include mathematical and relational operators that enhance the modeling capabilities for spatial analysis. Arithmetic operators include the basic functions of add, subtract, multiply, divide, but any quantitative operation can be developed. Relational operators such as greater than, less than, equal to, greater than or equal to, less than or equal to, and not equal to (>, <, =, >=, <=, <>) are also useful in limiting specific spatial conditions. Other more complex overlay techniques such as logical or Boolean operators are also available, although their utility is a topic for more advanced GIS applications.

Neighborhood Operations. Spatial primitives (points, lines, and polygons) are used to symbolize real world spatial features and locations in the mapping sciences. Six spatial relationships are employed in spatial queries and location analysis. Selected examples follow.

Point-Point. Is a given point within a specified location of another point, e.g. what is the distance and direction of a survey monument from a road intersection ? What are the geographic coordinates at a specified point? What is the distance between two or more points? What is the closest point to a given point?

Point-Line. Does a given point fall on a given line, e.g. does a survey monument lie on a highway bridge? What specific points fall on a given line, e.g. what springs are along a given traverse? List all points a given distance from a given line, e.g. show all spring locations <1000 m from the Blue River? What is the distance between a selected point and a given line, e.g. how far are the springs from the main channel of the Blue River?

Point-Area. List the points within a given polygon, e.g. where are the springs that discharge from the Salem Limestone Formation? Are a set of given points within a given distance of a polygon, e.g. where are the well locations that are within 1000 meters of the Raccoon Creek Group? Can a drainage basin (a feature) be seen from a given location (geographic coordinates)?

Line-Line. Do two lines intersect, e.g. does highway 30 intersect with highway 41? How close does one line come to another, e.g. how close is the Wabash River to Leatherwood Creek? Are two lines on the same plane, or is one above another, e.g. does Highway 41 physically cross Clark Street on the same plane, or is it an overpass? Display all streams that are connected to another stream?

• Line-Area. What streams cross (are within) a given geologic rock type? What are the names of the geologic formations (polygons) that a given stream crosses? Does a given road border a given geologic rock type?

Area-Area. What polygons overlap with another polygon, e.g. geology and soil types? What is the nearest unconsolidated rock unit to a given soil type? What areas are within a given area, e.g. show all soil units overlying the Morrison Formation?

Cartography, Remote Sensing, and Global Positioning Systems

Cartography is the science, art, and technology of making maps. A map is a graphic form of communication that illustrates spatial relationships typically modeled from the physical and human dimensions co-existing on the Earth. The International Cartographic Association defines a map as: "a representation, nominally to scale and on a flat medium, of a selection of material or abstract features on, or in relation to, the surface of the Earth." A printed map developed through traditional drawing processes is static, and cannot be changed unless it is redrawn and reprinted. When a map database is developed and stored in a computer file, all of the spatial data is directly accessible for upgrade and change. An output map product can be redesigned with the touch of a few keys on the computer keyboard through an automated process termed computer-assisted cartography. Automated (computer-assisted) cartography is employed in GIS, GPS, and remote sensing.

Nuclear reactions within the sun yield a full spectrum of electromagnetic radiation transmitted through space without major changes in its character. Remote Sensing is concerned with the measurement of selected wavelengths of electromagnetic radiation through multi-spectral sensing systems on board satellites and airborne platforms. An electrical (analog) signal is transformed into discrete or digital form with each pixel assigned a brightness value representing an average measure of electromagnetic radiation reflected or emitted from within its area. Grey level and color are assigned to create digital imagery that can be manipulated through digital image processing algorithms to enhance and better understand the interactive nature of processes operating to initiate changes in Earth surface features.

The global positioning system (GPS) is a satellite-based radio navigation system. The technology provides an accurate method of establishing location and elevation changes by measuring the time a signal is transmitted from the satellites to a GPS receiver located somewhere on the surface of the Earth. The degree of precision of these timed signals is obtained from an atomic clock on board each satellite, and is within fractions of a microsecond (1/1,000,000th of a second).


When combined as mapping sciences or spatial information systems (geomatics), the disciplines of GIS, GPS, computer cartography, and remote sensing form a formidable suite of processing tools employed by scientists studying the earth and environmental sciences and the manner in which humans interact with their planet.

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