What is GIS Flashcards
GIS is…
A way of spatially managing information
GIS is an information technology which means…
it organizes the data spaciely
The process is spatial but
it can be used to make scientific decisions
Spatial data uses a multiserver. What does this mean?
any data that can be mapped about the real world
Spatial data is multidimensional (xy) which means that…
data is usually stored as coordinates and topology.
why is important to have both Rastor and Vector data?
You can ask different questions with the different types of data
They may represent things but they are both structured differently and has consequences on how we analyse the world differently
What are the problems with spatial entities?
SCALE: How the real world is modelled depends on the scale of the modelling (e.g. generalization).
DYNAMICS: The real world is not static. For example, forests grow and are cleared, rivers flood, and cities expand = makes it poor for representing changing times = could change if GIS becomes fully online and updated but now this is a problem
DEFINITION (FUZZINESS PROBLEM): Many real world features simply do not fit into the categories of entities available (e.g. ill defined boundaries are common in nature)
If were always going to have these limitations we have to work with them rather than solve them- we need to get what we choose to represent right and then worry about things that are less important less
Whats the rule of a layer?
It can only be a vector or a rastor, it cannot be both. Also if it is a vector then it can only be dots or a line or a polygon
In rastor , every cell has to have a…
a value.
Takes up more storage by saying what something is and isnt rather than just what it is
= Vectors are more concise and have more storage
What is a network in a Vector?
where lost of points are connected
e.g. Contor lines on a map are vector
Why do we use Rastor more than Vector ?
because it is free and easily available – doesnt make it the best but it is the cheapest = were more used to working with rastor
= sometimes the details of the raster may matter even if we cannot see all the little squares
Rastor does not have an attribute table, explain it
Each value in a classified raster is represented with one row of an attribute table. This means that raster files have attribute tables, too, but instead of one row for each pixel, each group of pixels have a row.
What can vector layers be?
Can be dots, line or polygons
BUT
Not nessecerily true – a line and polygon are made of lots of points
In a polygon of a vector…
The first and last point should be the same
The computer knows if they are the same and will connect it if it is and will leave it a line if not
Vector VS Rastor maps
Vector – better for maps , because places are made of lines so vector has more of similarity for the things we are looking at
Rastor – not a good way of representing maps –it works because you can see it – depends on the purpose of which ones you’ll use
Explain types of Vector Data
A point is defined by a single pair of coordinate values.
A line is defined by a sequence of coordinate pairs defining the points through which the line is drawn
A polgyon is defined in a similar way, only with the first and last points joined to make a complete enclosure.
Are there curved lines in GIS?
There are no curved lines in QGIS because GIS records things as points – if they are connected then they are a line – the only way to get soemthing like a curve in vector is too zoom out
= to mimic a curve we put lots of points close together
What are the effects of changing things from raster to vector or vector to raster
this usually introduces mistakes and we struggle to find out what these mistakes are
what are the effects of Changing the resoltuion
If you increase the density of points in raster or increase the points in vectors the data is more specific but a lot of redundant information
How do we lie with maps ?
Depending on the resolution and whether we use vector and raster will determine the answer of what we are making = how we lie with maps = an apporximation of the real answer but nothing is abolsute
What happens when you transfer things from raster to vector or vector to raster ?
this usually introduces mistakes and we struggle to find out what these mistakes are
What are the types of spatial analysis?
Measurment ,Queires, spatial queries, Map overlay,map algebra,Map Algebra Boolean , Map Algebra Realtional ,Map Feedback
What are the effects of Changing the resoltuion
If you increase the density of points in raster or increase the points in vectors the data is more specific but a lot of redundant information
What should a map have?
Legend and Figure Caption. text Legibility ,Focus and Clarity, Color Scheme, Layer Organization, Source Citation,Inset, Communication and Simplicity, Context Information, Image Text and Alignment, Customization and Timeliness, Texts and Arrows,Neatness and Elegance
