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Intro GIS > Spatial Data > Flashcards

Spatial Data Flashcards

1
Q

What are the 2 types of data sources? describe the difference

A

primary sources are data collected firsthand

secondary sources are data collected by someone else

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2
Q

Describe metadata

A

information or data about spatial data
usually included along with a dataset to describe the data included

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3
Q

What type of information could be included in a metadata for a dataset?

A

extent of data
source of data
accuracy
scale
projection
explanation of codes used in the dataset

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4
Q

What are 4 examples of data collection devices for GPS and surveying?

A

tablets/phones
GPS
field notes
total station

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5
Q

What are the pros and cons of using tablets/phones as a GPS/surveying data collection tool?

A

pros: cheap, convenient/easy to carry
cons: not super accurate

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6
Q

What are the pros and cons of using a GPS device as a GPS/surveying data collection tool?

A

pros: more accurate spatial data

cons: more expensive

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7
Q

What are the pros and cons of using field notes as a GPS/surveying data collection tool?

A

pros: cheap, easy to write notes, convenient

cons: maybe less accurate

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8
Q

What are the pros and cons of using total station as a GPS/surveying data collection tool?

A

pros: very accurate and precise
cons: expensive

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9
Q

What are some examples of secondary data sources?

A

published maps
aerial photos
satellite images
social media
online sources like city open data portals

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10
Q

What are the 3 components of spatial data?

A

location - where
attribute - what
temporal - when

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11
Q

What are the 2 data models?

A

vector model (object)
raster model (field)

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12
Q

How do we represent spatial data?

A

with data models

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13
Q

What are data models? what are their functions?

A

they are representations of spatial data (with geometry and attribute data)

parameters for how real world events are stored in a computer

they function to control how data are stored and organized

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14
Q

How are spatial data conceptualized in a vector model?

A

as a collection of self-contained objects and their relationships

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15
Q

How are spatial data stored in a vector model?

A

spatial and attribute data are stored together

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16
Q

How many attributes can be stored for a single object or object layer in a vector model?

A

unlimited

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17
Q

What is an example of a vector model?

A

a model showing crime in the city of Vancouver

each data point is given a location, a category of crime, a date and time of crime, a police response, etc. and this is useful for analyses because it can help determine patterns

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18
Q

How are spatial data conceptualized in a raster model?

A

data are stored as pixels/cells each with a single attribute (value)

provides full coverage spatial data because there are no spaces between the pixels

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19
Q

How do vector and raster data models differ?

A

vector data are individual, self-contained objects which can be spatially separated
- models show the relationships between the objects
- an object can have unlimited attributes associated with it
- smoother maps
- represented as points, lines, polygons

raster data are pixels that are not separated in space (grids) and each pixel has a single associated attribute/value
- pixellated/blockier maps
- represneted by cells/pixels

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20
Q

What is an example of a raster model?

A

soil pH value across North America

every single pixel on the map has a single value (attribute) that gives the calculated/estimated soil pH for that pixel size

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21
Q

Describe vector data

A

vectors represent the world in layers
the layers can have points, lines, and/or polygons

a point can exist on its own (spatially separated) or be joined to other points to make a line

a line can exist on its own or be joined to other lines to make a polygon

layers can be used individually or combined

22
Q

Describe points

A

points are a vector data type which are
- 0 dimensional
- indicative of a location

ex. trees, houses, traffic lights, fire stations

23
Q

describe lines

A

a vector data type

1 dimensional geometry

composed of an ordered set of coordinates (multiple points joined - when joined, they’re called ‘nodes’)

order matters (ex. direction of water flow or road way)

sometimes called arcs

ex. major roads, one segment of a river, hiking trail, bike lane, water pipes, bus routes

24
Q

describe polygons

A

vector data

2 dimensional geometry

composed of an ordered set of point coordinates that create a boundary with the first and last point being the same = closed polygon

ex. forest inventory, lakes, census districts, watersheds, parks

25
Q

T or F: you can only use one vector layer at a time

A

false! you can use many

26
Q

What are attributes?

A

the ‘what’ of the ‘where’

the information providing context and value to the spatial data (location)

ex. tree height, tree species, average income in a census district, number of vehicles per hour on a street

also can be calculated - ex. distance to the nearest hospital, size of a watershed, road length

27
Q

how is attribute data stored?

A

attribute data are recorded during data collection and stored as attributes of the objects in the attribute table of the dataset

28
Q

What is the GIS?

A

a spatial database for spatial data
a representation of the real world

29
Q

What is a database?

A

an approach to organizing information in a computer environment

30
Q

What is a data matrix?

A

a classic database table (attribute table)

a column/row table with:

columns: object attributes
rows: spatial objects

31
Q

What 2 ways are data stored?

A

as vectors or as rasters

32
Q

the vector model is a ____-based model?

A

coordinate-based model (objects)

33
Q

Describe the raster model

A

composed of cells/pixels, each with a single value/attribute

34
Q

What type of data do rasters represent?

A

they can represent points, lines or polygons/areas, but most often used for continuous datasets because there are no spaces between pixels

35
Q

What is a common type of raster model?

A

3D elevation models

36
Q

How does raster data represent spatial data?

A

space is divided into units = pixels/cells –> tessellated in order to cover the surface with the same size and shaped cell

37
Q

T or F: raster cells have to square

A

false, they can be any shape as long as it creates a continuous surface but squares are the most common

38
Q

why are square rasters most common?

A

they are simple and easy to process or change size

39
Q

how are raster cell locations recorded?

A

not explicitly but stored relative to the origin and extent of the raster (like a cartesian coordinate system)

set an origin (0,0) and the extent of the raster, the grid will auto-populate

40
Q

Discrete raster vs. continuous raster

A

discrete: integer values, whole numbers
- pixels with the same value are in the same class/category
- class values have no ranking (ie., 2 is not better or more than 1, just different class)
- similar to polygons
- ex. soil classes, vegetation classes

continuous: real values (decimals), infinite values possible
- each value is unique and not representative of a class (ie., if there are more than one values of 1.2, they are not necessarily the same class, just same value)
- called a surface
- ex. elevation, precipitation

41
Q

Describe the digital elevation model (DEM) and what type of data it stores

A

a common continuous raster model

height (elevation) is the attribute stored for each cell in the model

the legends are usually represented as a single range/gradient

42
Q

What happens when you convert a vector to a raster?

A

the smoothness of the data is lost, the rasterized data becomes much blockier

details are lost - vectors include many attributes and rasters only one
precision is lost - ex. a vector point is a specific location, when rasterized this point becomes a square cell (the point may be anywhere in the cell)

43
Q

What is resolution?

A

the size of a square raster pixel = x (ex. 25m x 25m cell is a square with sides, x, = 25m)

the area of the pixel is then 25m x 25m = 625 m2

44
Q

How is the resolution or size of the raster pixels used to determine area of a polygon on a map?

A

the resolution of a pixel is used to determine the area of that pixel and multiplied by the number of pixels with that same value to give the area of the polygon

ex. a cell with a 25m resolution has an area of 625 m2 (25 x 25) so if there are 30 cells with 25 m resolution, then the polygon has an area of 18 750 m2 (25 x 25 x 30)

45
Q

how does the amount of data change when the raster resolution is changed?

A

if a pixel size is doubled, the new pixels include 4 times the area per pixel

46
Q

How do smaller raster cells compare to larger cells?

A

smaller:
- higher resolution = more details
- higher spatial accuracy
- slower display
- slower processing
- larger file size

larger:
- lower resolution = less details
- lower spatial accuracy
- faster display
- faster processing
- smaller file size

47
Q

Give an example of how spatial accuracy changes with raster resolution

A

at 80km resolution, BC has 114 pixels = 80km x 80km x 114 pixels
= 729, 600 km2 area

at 20km resolution, BC has 2296 pixels = 20 x 20 x 2296
= 918, 400 km2 area

BC has an actual area of 944, 735 km2

larger cells provide a much lower / less accurate estimation of the area of BC and a lower resolution map

48
Q

Why does resolution matter?

A

you can’t see more than what is present in a single pixel

you can’t make the resolution finer than what it was when collected

it is a limiting factor in calculations - the results can only be as accurate as your least accurate dataset (lowest resolution dataset)

49
Q

T or F: raster and vector datasets can be combined and displayed together on a map

A

true, but they need to be converted into the same data format (either both raster or vector)

50
Q

Which data format is better, raster or vector?

A

it depends on your data and purpose, but usually vector because it includes more information/attributes

Intro GIS (1 decks)

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