Midterm 1 Flashcards
(35 cards)
Define GIS and GPS
GIS= geographic information system- a type of software that maps, analyzes and retrieves location-based data GPS= Global positioning system- using satellites to get info on a location in real-time
Define remote sensing and give different examples of it.
It is the acquiring of data/imagery using 2 methods:
1) Satellite imagery
2) Aerial photography (airplanes)
What 3 things relate vector objects to each other. (topology)
- Adjacency- when a common boundary is shared btwn 2 polygons
- Connectivity - how lines intersect w one another
- Containment - how locations are situated inside a polygon boundary
Describe the 2 types of conceptual models.
- Discrete= when the world is made up of a series of objects, each w a fixed location/boundary/starting and stopping point
- Continuous field = not everything has a fixed boundary, a surface made up of near
- infinite set of points
- values available at all locations on the field
What are the 2 data models and what conceptual model do they each naturally arise from?
- Vector - arises naturally from discrete objects, represents real world info w points, lines and polygons (vector objects)
- Raster- arises naturally from continuous fields, represented with pixels (grid cells)
Define topology.
How objects connect/relate to each other independently of the objects’ coordinates
(ex. you need info that an intersection is needed where 2 lines cross)
* stays the same no matter how the map is distorted
Define attributes.
It is the non-spatial data that’s associated w a spatial location (ex. age, material, owner etc. of a location)
How are attributes categorized by their data levels? List, describe and give examples from lowest to highest.
nominal data- values that represent a unique identifier, difference btwn numbers is not significant (ex. names of locations)
ordinal data- a type of data that refers solely to a type of ranking (ex.low, medium, high- categories)
interval data- a type of numerical data in which the difference between numbers is significant (addition and subtraction is meaningful), but there is no fixed non-arbitrary zero point associated with the data
ratio data- a type of numerical data in which the difference between numbers is significant, but there is a fixed non-arbitrary zero point associated with the data
What is an attribute table and what do you call the rows and columns in this table?
attribute table- a spreadsheet-style form where the rows consist of individual objects and the columns are the attributes associated with those objects
records- the rows of an attribute table
fields- the columns of an attribute table
Define metadata. Why is it important?
metadata = “data about your data”
- answers question about data (ex. what the fields in the attribute table actually represents, how/when it was created, accuracy of data etc.)
- meta = “along with”
What is the difference between a geographic and a cartographic/map scale?
geographic - “real-world” size of an area
cartographic - x number of units on a map equal y number of units in the real world (the smaller the y (larger the denominator), the larger the scale)
Define a representative fraction (RF)-determines cartographic scale. Under what conditions would it be a poor choice for representing map scale?
RF= the ratio/fraction that determines how many units of x on a map equals how many units of y in the real world
If you change the size of the map, you also change the scale. So if you are unable to control the output of the map, this would be a poor choice.
Difference between large-scale and small-scale map according to RF and geographical area.
large-scale maps- have a larger RF value (largest map is 1:1) and a smaller geographic area.
small-scale maps- have a smaller RF value (ex. 1:250,000) but a larger geographic area.
What properties define a raster data model?
- can only assign a single attribute per entity
- Several raster layers would be needed
- Simple file structure
- Takes up much more storage space bc:
1. Many entities per layer
2. Often many layers - Does not support topology
- Remote sensing = always in the form of rasters
- efficient at spatial processing bc all the pixels can move from one layer to the next
- Does not have a fixed cartographic scale
What properties define a vector data model?
- More than one attribute per entity
- (ex. For a ski lift we can store how it was built, what its built by, who built it etc.)
- Less storage space for 2 reasons:
1. Fewer entities per layer
2. Often fewer layers - Does support topology bc we do not rely on entities being attributed properly
- Vector file structures are more complex *- uses a series of files which is then related to one another
- when you want to grab a vector database, you have to grab ALL of the vector databases*
What are the three expressions of Map Scale?
(Remember scales are never completely accurate bc a 3D world is communicated in 2D but have an impact on the detail of a map)
RF= representative fraction = the ratio of map distance to ground distance (useful for performing calculations)
Verbal Statement= describes relation btwn map distance and ground distance (ex. one mm on the map = 5 km on the ground)
Bar (graphic) scales = a “bar” that relates map distance with ground distance (shrinks and grows along with the map)
Does a GIS database have a scale?
No because GIS database consists of many scaled maps therefore there is not a scale for the database itself.
Define spatial resolution.
It is the size of the smallest recording unit OR the smallest size of a feature that can be mapped/measured
(ex. a pixel in a raster data model)
It has an impact on cartographic generalization.
Define cartographic generalization and specification (how is it affected by specification)
A function of scale that is specified by cartographic guidelines.
specification = defines how real features on the ground is represented on a map (ex. inclusion/exclusion of certain features, simplified guidelines etc.)
Determine how accuracy is affected by precision and bias. Define the differences.
Accuracy = closeness to the truth and is a function of precision and bias
Precision = level of exactness in observations/representations (precise = clustered data, imprecise = scattered data)
Bias= the systematic distortion in measurement/observations bc of the operator/equipment
(biased = off-center/less accurate, unbiased = more accurate/centered)
*The averages of biased data will never be true/accurate
Define a polyline and how it is related to the weakness of Vector conceptual models.
A polyline is a curved line made out of many straight line segments.
Vector model = inefficient w curved lines
Can continuous fields be represented by vector data?
Yes by using contour lines (isolines) which traces the same value across the landscape
- You lose some detail and force the audience to interpolate/guess what is between the lines
(interpolate= to make an educated guess for an unknown value)
List 2 important uses of topology and what format it cannot be stored as.
- Maintains data quality and storage efficiency
- Performs certain analytical operations
* * cannot be stored as a shape file
What are the 8 elements of a map? Which element is not always needed?
- Frame and/or Neatline
- Map Body
- Inset/overview (not always needed)
- Title/subtitle
- Legend
- Data source, authorship, metadata
- Scale (RF, Verbal, Graphic)
- Orientation (graticule, north arrow, compass rose)
