W2 Flashcards
What is nominal level data
identifies one entity from another (categories)
- ex. vegetation
- not ranked or quantified
What is ordinal level data?
Data is ranked along a scale
- cannot apply arithmetic operations
What is interval level data?
Data values are quantitative and are on a measurement scale based on a arbitrary zero point (ratios between values do not make sense)
- ex. temperature scale and longtitude
What is ratio level data?
Data values with a true origin
- ratios between values make sense
- ex. distance
What are the three data types stored in GIS
Integers, floating point values, strings
How are numbers arranged in the binary system?
In columns that represent powers of 2
How many bits in a byte
8
- sometimes a bit is reserved to store the sign (+/-) (this is called a signed byte
What are several bytes strung together called?
a word
How does the binary system work
All computations are carried out using binary arithmetic
Electronic circuits can represent and process data using binary signals, where “on” represents 1 and “off” represents 0.
How many numbers can be represented in a byte
256
What are the two types of integers and how many bytes do they have?
short (2 bytes)
long (4 bytes)
How many bytes can floating point value data have
4 or 8
What is precision in terms of bits
Precision is a function of # of bits used to code the word
How many bytes does string data have?
Each character is stored as one byte (takes up alot of memory)
Why would be integer data be better than float?
- to keep storage size small if higher precision is not required
Define geographic scale
general scope or extent of things
Define cartographic scale
Scale of a feature on a map with respect to the real world a map
Define data scale
Data is collected or digitized at some scale or resolution
What is resolution
Smallest details that can be distinguished in a dataset
What dictates scale for vector data
precision of coordinates
What dictates scale for raster data
resolution
What are some issues with converting data from raster to vector
- Needs a lot of storage
- Can look shaky (you can smooth it but will create distortion)
What are some issues with converting data from vector to raster
Depending on scale you might lose precision
Describe latitude and longitude
- metric, standard, stable
- Uses a well-defined and fixed reference frame
- most universal and commonly adopted system of referencing global geographic locations
- has the potential for very fine spatial resolution
- supports other forms of spatial analysis
What is a great circle
shortest distance between two points
- due to sphere shape this is actually a curved line
Define datum and ellipsoid
Ellipsoid: approximates the geoid (shape of earth)
Datum: defines the position of the ellipsoid on the earth (means that different datums mean two different coordinate values)
What are projections
Method of converting geographic space to cartesian space
- need to portray the curved surface of the earth as a flat (map) surface
- described by parameters
