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Intro GIS > Spatial Data > Flashcards

Spatial Data Flashcards

(50 cards)

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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

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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

Study These Flashcards
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

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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

Study These Flashcards
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
T or F: you can only use one vector layer at a time
false! you can use many
26
What are attributes?
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
how is attribute data stored?
attribute data are recorded during data collection and stored as attributes of the objects in the attribute table of the dataset
28
What is the GIS?
a spatial database for spatial data a representation of the real world
29
What is a database?
an approach to organizing information in a computer environment
30
What is a data matrix?
a classic database table (attribute table) a column/row table with: columns: object attributes rows: spatial objects
31
What 2 ways are data stored?
as vectors or as rasters
32
the vector model is a ____-based model?
coordinate-based model (objects)
33
Describe the raster model
composed of cells/pixels, each with a single value/attribute
34
What type of data do rasters represent?
they can represent points, lines or polygons/areas, but most often used for continuous datasets because there are no spaces between pixels
35
What is a common type of raster model?
3D elevation models
36
How does raster data represent spatial data?
space is divided into units = pixels/cells --> tessellated in order to cover the surface with the same size and shaped cell
37
T or F: raster cells have to square
false, they can be any shape as long as it creates a continuous surface but squares are the most common
38
why are square rasters most common?
they are simple and easy to process or change size
39
how are raster cell locations recorded?
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
Discrete raster vs. continuous raster
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
Describe the digital elevation model (DEM) and what type of data it stores
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
What happens when you convert a vector to a raster?
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
What is resolution?
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
How is the resolution or size of the raster pixels used to determine area of a polygon on a map?
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
how does the amount of data change when the raster resolution is changed?
if a pixel size is doubled, the new pixels include 4 times the area per pixel
46
How do smaller raster cells compare to larger cells?
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
Give an example of how spatial accuracy changes with raster resolution
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
Why does resolution matter?
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
T or F: raster and vector datasets can be combined and displayed together on a map
true, but they need to be converted into the same data format (either both raster or vector)
50
Which data format is better, raster or vector?
it depends on your data and purpose, but usually vector because it includes more information/attributes

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