feature: A feature is a geometric object that represents something in the real world on a map. Examples are polygons that represent areal features like states, counties, and water bodies; lines that represent linear features like roads and streams; and points that represent features like cities, police stations, or polling places. Some features like cities are represented differently based on the scale of the map, as points on a small scale map and as polygons on a large scale map.
feature class: A feature class is a collection of features that all have the same kind of geometry (polygon, line, or point). A feature is a single instance of a feature class. For example, I have a feature class named usStates.shp. In the usStates.shp feature class there are 50 features, one for each state. Each state is represented by a polygon.
attributes: In the usStates.shp feature class there are 50 features, one for each state. Each state is represented by a polygon and each polygon has attributes, which are distinct properties of each individual state, like 'name', 'area', and 'population'. Here's a small example of a feature class attribute table:
The entire table represents the feature class. each row is an individual feature (or rowor record). Each column is an attribute(or columnor field).
layer: Each map layerdisplays a feature class with a defined symbology. For example, I have a map layer named 'States'. the layer displays a feature class named 'usStates.shp', and each feature is symbolized by a color fill that increases in intensity based on the value of the attribute 'pop2014'.
group layer: A group layer is just a container for a group of similar layers. An example would be a group layer named 'Places' that contains layers named 'Cities', 'Counties', and 'States'. You can turn the whole group on or off, but you can't symbolize a group layer.
qualitative (or categorical) vs quantitative (or numeric) attributes: A qualitative attribute is normally a text value that places something in a category, for instance cars can be red, blue, or green, people can be tall or short. You can compare cars on whether they are red, blue, or green, but it makes no sense to say that red is greater than or less than blue. You can compare states based on population and in that case it does make sense to say that New York's population is greater than South Carolina's.
map symbology: In our example layer named 'States', a state can have the attributes 'sub_region' and 'pop2010', and the states can be colored on a map by the 'sub_region' attribute with all southern states being one color, all middle atlantic states having another distinct color, and so on. That would be a qualitative or categorical comparison. The states can also be colored in varying shades of the same color, with the intensity of the shades corresponding to a numeric attribute like 'pop2014': That would be a quantitative or numeric comparison.
In this example map darker colors represent more population and lighter shades represent less population. Cities have a population field and are represented as circles of varying size based on their population.
normalization: When you normalize data, you express a quantity as a proportion of another quantity. An example is population. Instead of coloring map polygons by population, you can divide population by map unit area and show population per unit area (usually persons per square mile). You can also show population as a percentage of a total by dividing a population count by the total population, like seniors as a percentage of all persons.
query: A query is a request to a database to produce a table of all rows meeting only certain criteria. an example in SQL would be "SELECT * FROM usCities WHERE pop2014 >100000", which would produce a table only of cities with a population greater than one hundred thousand. When you create a definition query in ArcGIS, you're specifying just the WHERE clause in a SELECT query.
scale: Map scalecan be expressed in three ways. A verbal scale states in words the relationship between a map distance and a ground distance, such as '1 inch = 2000 feet'.
You can also place a scale bar on the map and indicate that one division of the bar equals some number of ground units. This is especially useful if the map may be copied and either reduced or enlarged in size. This second type if scale is called a graphical scale.
The third type of scale is called a representative fraction or ratio scale. The scale is stated as a dimensionless ratio like '1:24000', meaning that one unit on the map equals 24,000 of the same units on the ground, or in other words that a given feature on the map is one twenty four thousandth the size it is in real life.
If the dimensionless ratio represents a small fraction, like 1/2,000,000, then the map is 'small-scale', features shown on it are relatively small, and the map shows a relatively large area.
If the dimensionless ratio represents a large fraction, like 1/1,200, then the map is 'large-scale', features shown on it are relatively large, and the map shows a relatively small area.
This precise geographers' definition can sometimes be confusing because in ordinary speech the terms may be reversed, with many people saying that a large-scale map is one that shows a large area, and a small-scale map is one that shows a small area.
Notice that all of these examples refer to the same scale. Saying that 1 inch = 2000 feet is the same thing as saying that 1 inch = 2000 x 12 = 24000 inches, or 1:24000.
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