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G.I.S. > Modelling the world in G.I.S. > Flashcards

Modelling the world in G.I.S. Flashcards

1
Q

How can we model reality?

A

We can use vector geometry.

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2
Q

What is a point?

A

The simplest form of vector geometry which has an x and y coordinate to say where abouts it is in the world.

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3
Q

A point can also have a third piece of information when looking at coordinates, what is this and what does it mean?

A

The z value and that is the height above sea level.

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4
Q

What can we use context for?

A

To give spatial information more meaning for example by adding a background map.

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5
Q

What could a point represent?

A

A house and we would denote a house symbol etc.

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6
Q

What do we use to give meaning to coordinates for interpretation purposes so people understand what information they contain?

A

Symbolisation

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7
Q

What could you model Newcastle as?

A

A point or as an area.

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8
Q

What is vector data modelling associated with?

A

Location where we encode more information, for example we could add the address of a house or postcode,

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9
Q

We can start associating this information for each house what do we call this?

A

Attribute information and you store it in an attribute table.

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10
Q

What is the attribute information for a house?

A

1) House number
2) Post code
3) House price
4) Council tax band

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11
Q

When could attribute data have a negative impact?

A

When information is shared about what time of the day you leave the house and when you come back, impacting privacy.

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12
Q

When do you get a spatial data layer?

A

When you start creating collections of features with a set of shared attribute types.

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13
Q

What do most coordinate systems consider when calculating spatial relationships?

A

They consider the world to be a two-dimensional grid, just like a piece of graph paper allowing us to measure between two points and use Pythagoras.

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14
Q

What happens due to the earth being globular?

A

When measuring larger distances you get problems because of the curvature of the earth.

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15
Q

True or false, “you can use all coordinate systems for large areas”

A

False, you can only use certain coordinate systems for small areas where we can consider the world to be flat.

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16
Q

What are latitude and longitude?

A

They are the measurement of an angle from the centre of the Earth, it makes distance calculation very complex and less accurate.

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17
Q

What is it called when point and attributes join together in sets?

A

A layer or a feature class.

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18
Q

What is another way we can model our data?

A

Is through thinking about it as a line.

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19
Q

What do we model a line as?

A

As a set of coordinates, but we don’t model the coordinates all the way along it we only store information whenever there is a change in direction.

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20
Q

Do the coordinates along a line have an order to them?

A

Yes, a start and an end and that is how we model any of those features such as roads and railways.

21
Q

When we have a number of lines what do we have?

A

A feature class.

22
Q

What does a feature class share?

A

Shares a geometry type and a set of attributes with everything else in that feature class.

23
Q

What are maps for navigation all about?

A

Linear features

24
Q

What can you do thematically to display a road?

A

Change the colour of it and change its widths depending on it.

25
Q

On an ordinance survey map what is a minor country and what is a really small road denoted as?

A

Minor country road- yellow line

Really small road- grey line

26
Q

What is a polygon?

A

It is an enclosed shape, an irregular shape and this is the other way in which we model any other geometry from using vector modelling.

27
Q

What are the 3 ways we model geometry using vector modelling?

A

1) Points
2) Lines
3) Polygons

28
Q

What could a polygon represent?

A

A building or agricultural fields or countries.

29
Q

What must a map contain?

A

Must contain meta-data or relevant explanation.

30
Q

How do we define a polygon?

A

By its boundary and we model it in the same way we model a line. For example start at one of the corner and every time we change direction we store a coordinate and we finish by storing another coordinate where we started.

31
Q

What do we use to represent a quantity associated with an area or polygon?

A

Pie charts

32
Q

How can we model the weather?

A

Start off with a square called a cell or a grid cell and in that cell we add one piece of information which is always a number. This square also represents a physical amount of area which is called the spatial resolution.

33
Q

What happens as you increase or decrease your resolution?

A

You exponentially increase your storage requirements.

34
Q

What is it called when we combine cells together?

A

Grid pattern

35
Q

What is land use map a good example of?

A

Continuous information in the form of a category not a number.

36
Q

What does a land use map say?

A

It say what the land is being used for e.g. agriculture, building or roads. therefore the number inside of the cell represents a category instead of a measurement

37
Q

What is a digital elevation model?

A

Where the number represents the height of that grid cell above sea level.

38
Q

How can we model the world?

A

Through discrete features; points, lines and polygons that we attach attributes to. And modelling continuous surfaces using grid cells. Where a cell either represents a quantity or a category.

39
Q

Know what vector data and raster data looks like.

A

Look on lecture 3.

40
Q

Define spatial resolution.

A

The length of one cell.

41
Q

What does it mean if you say “a cell has a spatial resolution of 5m”?

A

One cell represents 5m in the real world.

42
Q

Typically for Arial photography what is the spatial resolution?

A

Roughly 2cm.

43
Q

Typically for satellite data what is the spatial resolution?

A

1m up to 50-100m.

44
Q

What is raster data stored the same as?

A

Image data

45
Q

What is a picture?

A

A set of numbers, where the numbers refer to a grey scale.

46
Q

What do we use for coloured images?

A

The RGB index (Red, Green, Blue).

47
Q

What are all images made up of?

A

3 layers; a red layer green layer and a blue layer and there is and a value for each layer. The values go between 0 and 255 for each layer.

48
Q

Why do we sometimes what a single intensity layer?

A

Because vegetation shows up better under certain colours.

G.I.S. (7 decks)

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