Modelling the world in G.I.S. Flashcards
How can we model reality?
We can use vector geometry.
What is a point?
The simplest form of vector geometry which has an x and y coordinate to say where abouts it is in the world.
A point can also have a third piece of information when looking at coordinates, what is this and what does it mean?
The z value and that is the height above sea level.
What can we use context for?
To give spatial information more meaning for example by adding a background map.
What could a point represent?
A house and we would denote a house symbol etc.
What do we use to give meaning to coordinates for interpretation purposes so people understand what information they contain?
Symbolisation
What could you model Newcastle as?
A point or as an area.
What is vector data modelling associated with?
Location where we encode more information, for example we could add the address of a house or postcode,
We can start associating this information for each house what do we call this?
Attribute information and you store it in an attribute table.
What is the attribute information for a house?
1) House number
2) Post code
3) House price
4) Council tax band
When could attribute data have a negative impact?
When information is shared about what time of the day you leave the house and when you come back, impacting privacy.
When do you get a spatial data layer?
When you start creating collections of features with a set of shared attribute types.
What do most coordinate systems consider when calculating spatial relationships?
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.
What happens due to the earth being globular?
When measuring larger distances you get problems because of the curvature of the earth.
True or false, “you can use all coordinate systems for large areas”
False, you can only use certain coordinate systems for small areas where we can consider the world to be flat.
What are latitude and longitude?
They are the measurement of an angle from the centre of the Earth, it makes distance calculation very complex and less accurate.
What is it called when point and attributes join together in sets?
A layer or a feature class.
What is another way we can model our data?
Is through thinking about it as a line.
What do we model a line as?
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.
Do the coordinates along a line have an order to them?
Yes, a start and an end and that is how we model any of those features such as roads and railways.
When we have a number of lines what do we have?
A feature class.
What does a feature class share?
Shares a geometry type and a set of attributes with everything else in that feature class.
What are maps for navigation all about?
Linear features
What can you do thematically to display a road?
Change the colour of it and change its widths depending on it.
