GIS Exam 1

File management

Maintaining a logical folder and file structure for your working files/folders and keeping all folders/files for one project in one place

Pathname

The file path that leads to where the file in question is located

Absolute pathname

The complete location of the file all the way to the file location of origin

Relative pathname

Where the file is with respect to the active working directory

Nest folders within folders

Create other folders within the main folders as the need arises

Qualitative data

Nominal or categorical data

Numerical data

Quantitative: interval and ratio

Nominal data

Names or uniquely identifies objects. Each feature is likely to have its own value. Usually portrayed on the map as labels

• State names

• Owner of parcels

• Tax ID number

• Parcel ID number

Categorical data

Names or describes objects. The data labels are categories. Data within a map may fall into a few groups or they may have as many values as featured

• Hair color

  • Brown, blonde, black, red

• Smoking status

  • Smoker or non-smoker

Ordinal data

A type of categorical data in which order is important though the interval between values is not constant

• Class

  • Freshman, sophomore, junior, senior

• Opinions about politics

  • Unhappy, neutral, happy

• Comfort level

  • Cool, cold, freezing

Quantitative or Numeric data

Can be represented by using several different types of maps including graduated color or symbol, dot density, or chart maps. The ranking of the data is important. The type of data has number values like:

• Population

• Rainfall

• Age

• ACT score

• Number of students in class

Discrete data

Measurement data where only certain values are possible. There is a gap between values

• ACT scores

• Number of caves in BG

• Number of students in GIS316

Continuous data

Any value within an interval is possible with a fine enough measuring device. Typically use isoline maps

• Elevation on a topographic map

• Cholesterol over time

• Temperature during a 24 hour period

• Water temperature

Interval data

Data are spread along a regular scale of measurement units, like along a ruler or thermometer for measuring temperature. Measurement scales are expressed in equal number units, but do not have a true zero point

• Achievement tests

• Degrees

Ratio data

Measurement scales expressed in equal number units, but having a true zero point. Cannot be a negative number

• Test scores

• Salaries

• Weight

• Distances

• Precipitation

Single symbol map

All of the features are drawn using the same symbol. This type of map is used to show the size, shape and location of the features

Nominal maps

Assign a different color to every unique value in a field

Quantities maps

Symbols in a quantities map represent a range of numeric values, like population. These maps usually show interval and ratio data and may also be used to display ordinal data

Graduated symbol maps

Group data into distinct classes and represent each class with a different sized symbol

Proportional symbol map

Directly scales the size of each symbol based on the exact value of the data at each location without grouping classes

Dot density maps

Visually represents the geographic distribution of a phenomenon by placing dots on a map, where each dot represents a specific quantity of that phenomenon

Isarithmic map

A thematic map that uses lines to connect points of equal value for a continuous phenomenon

Contour map

A map connecting lines of qual physical election. Used to map physical geographical height and depth.

Spheroid

A three-dimensional solid in which all points on the surface are the same distance from the center. Used to approximate the true shape and size of the earth. In GIS this term and ellipsoid are used interchangeably

Map units

The actual units used in the measuring (meters or imperial)

Extent

The range of the x-y values

Unprojected (Geographic coordinate system GCS)

Based on spherical globe coordinates. Uses degrees of latitude and longitude

Projected

Converts spherical coordinates to planar coordinates. Set of mathematical equations. Projects 3D coordinates to 2D map

Latitude

Measures the angle from the horizontal. It represents north-south distance from the equator

Longitude

Measures around the circle of the equatorial plane. It represents east-west distance from Prime Meridian

Standard parallel

A specific line of latitude on a map projection where the scale is completely true and free of distortion

Tangent projection

Touches the globe at a single line, giving it one standard parallel

Secant projection

Slices through the globe at two lines, giving it two standard parallels

Prime Meridian

The imaginary north-south line that defines zero degrees longitude, dividing the Earth into the Eastern and Western hemispheres. Longitude is zero

Central meridian

An imaginary line of longitude that defines the center and serves and the starting point for horizontal measurements in a map projection or coordinate system

Normalizing data

Converting raw value into a proportion, rate, or ratio by diving it by some other relevant quantity, usually total population, total area, or another baseline count so that values become comparable across units of different size

Classified map

Values grouped into a set number of discrete classes (e.g. 4-6 bins). Limited number of distinct colors

Unclassified map

Every unique value gets its own shade, no grouping

Project tool

Converts a dataset’s coordinates from one spatial reference to another, producing a new output feature class, feature dataset, or raster

Developable surface

A geometric form capable of being flattened without stretching or tearing, such as cylinder or cone, and a plane

Graticule

The intersection of latitude and longitude lines make a graticule

Large scale map

A map that shows a relatively small area with a high level of detail

Small scale map

Map that shows a large geographical area with less detail, meaning it covers a wider region but its features are depicted with less precision.

Projection

The process of projecting the earth onto a flat surface

Distance (equidistance)

Whether the map preserves true distances, but only along certain lines, usually from one or two central points or along particular meridians. Used when the primary concern is accurately measuring distances from a specific point or along specific lines

Area (equivalence)

Whether regions maintain their correct relative size. An equal are projection like Albers or Mollweide preserves area accurately, which matters a lot for thematic mapping

Direction (Azimuthal)

Whether bearings/directions from a point are shown correctly. Preserve direction from one central point outward, which is useful for things like flight paths, or seismic/radio proportion maps

Shape (conformality)

How well angles and local shapes are preserved. A projection like this like Mercator keeps small shapes looking correct, which is why it’s still used for navigation, a straight line on the map is a straight compass bearing

Class

The overall shape and appearance of the graticule after the projection process is complete. Three classes are cylindrical, conic and planar

Cylindrical class

Wrapping developable surface around a cylinder, projecting the graticule, then unrolling the cylinder

Conic class

Results from wrapping the developable surface around a cone, projecting the landmasses and graticule on the cone, then unrolling the cone

Planar class (or azimuthal)

Results from positioning the developable surface of a plane next to the reference globe and projecting the landmasses and graticule onto the plane

Secant case

The developable surface passes through the reference globe

Aspect

Deals with the placement of the projection’s center with respect to the Earth’s surface

Equatorial

Centered somewhere along the equator

Oblique

Centered somewhere between the poles and the equator

Polar

Centered at one of the poles

Transverse aspect

Means the projection surface is rotated 90 degrees from normal

Tissot’s Indicatrix

Provides a graphical representation of distortion at various places across a projection

Equidistant projections

These maintain the principal scale from two points on the map to any other point on the map

Conformal projections

These preserve the angular relationships around a point by uniformly preserving scale relations about that point in all directions

Azumithal projections

Directions are preserved from the center of the map to any other point on the map in these types of projections

Compromise projections

Do not preserve any specific property