Computerization Flashcards
What is data?
Values of qualitative or quantitative variables belonging to a set of items. Individual facts, statistics, or items of information
How is data organized?
Most data are placed into some context that underlies their structure
.
Most of these constructs are linear in nature (one-dimensional).
Data items are laid out in a list of some sort (more later) with a beginning that progresses linearly to an end.
Data items may be numbers or characters, dates, etc.
Data items may repeat in the list.
The actual sequence of the data may not be significant, or may be very significant (more later as well)
What is a database?
A database is an organized collection of data, today typically in digital form. The data are organized to model relevant aspects of reality (for example, the availability of seats on planes), in a way that supports processes requiring this information (for example, finding a flight with window seats).
What does a database typically do?
Typically puts lists vertically into tables, in which each column is a list, and each row is an object (it has an identity - such as a company in the example). Care mustbe taken that the lists all“line up” by row.
What is spatial data? What does it require? What do we adapt to create spatial data? What do
The big jump into spatial data from lists is the addition of multiple dimensions. Spatial data (like maps transformed from reality) require at least two dimensions since “location” is an important (likely critical) aspect of meaning.
We adapt coordinate systems to create spatial data models.
What does spatial data have to store?
An attribute of location among other attributes. Maps are a good example of this. On maps, location is shown by position on page, for “data” we need to measure coordinates
Why do we need spatial data?
The data that is stored in a one-dimensional list. If we knew the location of each part of the data it could help us gather information. It gives us a different understanding that we cannot get from linear data.
What are the three things spatial data require?
1) Require consideration of measurement types (as do list data)
2) Require appropriate modeling by appropriate geometric dimension
3) Require appropriate consideration of variation across space.
What is all data?
Measurements.
What is nominal data?
Nominal data have names only: qualitatitive differences are recognized only.
Mathematically: = <>
Examples: Voting by party, Soils, Land cover, Male/Female
What is ordinal data?
Ordinal data are the lowest level of quantitative data in that they give implied rank through names.
Mathematically: = <> > <
Example: high, medium, low : near, far : more, less: strongly agree, agree, neutral, disagree, strongly disagree
What is interval data?
Interval data use numbers and amount of difference between numbers, but have no “0” that is meaningful. “0” is usually an arbitrary value used for convenience.
Mathematically: = <> > < + -
Examples:
Time
Temperature
Earth Grid systems
What is ratio data?
Ratio data use numeric scales like interval, but in this case “0” means “none”.
Mathematically: = <> > < + - / *
Examples: Counts of most anything Age: Intervals from an interval scale (subtractions) Distances, areas Percentages Densities
Spatial data have______
Dimensionality. For mapping and databases, we use a geometric transformation from reality to a database representation. We recognize that we can use simple geometric analogs to reality in making a database of spatial data: Points, Lines, Areas. Surfaces/Volumes
What are point objects?
0 dimension.
Locate features that either:
1) take up no space on Earth (true points): survey locations, graticule, crossings such as that at Four Corners, NM
2) take up a small space at the scale of the map (cartographic points): cities, buildings,utility poles
What are line objects?
1 dimension
Represent features that are extremely long compared to their width. May be:
1) true lines that have no width on Earth: all survey boundaries: national, state, county, or property, contour lines, graticule lines
2) cartographic lines that have width on Earth, but we do not choose to maintain it on the map. This choice is a function of scale, roads, streams/rivers
What are area objects?
Two dimensions
Used for features that have discernible length and width at the scale of the map. Features can be of several types based on variation and on measurement level.
What are surfaces?
2.5 Dimensions
Most GIS applications do not use true 3D coordinate systems (X, Y, Z) for location, they use a map attribute for the third dimension – so we consider surfaces 2.5D. We place an attribute at each (X,Y) location.
A calculation based on scale and dimension: At 1 inch to 1000 feet, 300 feet is______.
0.333 inches
Surface models vary across _______
Space.
Because surface models collect data “everywhere” to form the surface, there are some issues to consider when deciding to model a surface. What are these issues?
At what density do we want to provide information (usually called the resolution)?
How do the values vary from place to place? Are they continuous (spatially dependent on values at neighbors)? Are they discrete (spatially less dependent on values at neighbors)?
What are discrete surfaces?
Discrete surfaces are not predictable by space, data must be collected everywhere, but there a finite number of locations that
have data - (e.g. SALES TAX RATES BY STATE)
Observed by noting that neighboring areas do not necessarily have similar values
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What are continuous surfaces?
Continuous surfaces are somewhat predictable by space, data may be collected anywhere, and there are an infinite number of locations that have unique data - (e.g. TEMPERATURES)
Observed by noting that neighboring locations have similar values.
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What is spatial autocorrelation?
If a particular variable like elevation is spatially autocorrelated, the values nearer a measured location are closer in value to that at the measured location and those farther away are likely farther in value from that at the measured location.
A key purpose of GIS database design is to use the GIS to retrieve data efficiently. We can use GIS to do ________ based on fields in a table, but also to do retrieval based on spatial geometry________. That is a large part of the power of GIS.
standard attribute queries
spatial query
What are the two approaches of streamlining GIS database?
Simple lists are suited for data that have to be used in a particular sequence or they lose their meaning (book text, movie frames, lines in vector GIS – later), or for small databases.
Ordered lists are used to speed up the search process when the initial data sequence is not important and the data order can be changed.
What are simple lists?
Simple lists have only one sequence inherent in them: top to bottom. Items in a list may not have an underlying internal order, and may not need one.
A shopping list is a good example. What is the order on a shopping list?
For a simple list, what is the formula?
int(log(n)/log(2))+1
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