Spatial Data /raster Flashcards
True or false : GPU is bigger than a CPU because it is computing in parallel
True
True or false m the more RAM you have the more apps you can open simultaneously
True
What happens if you have less RAM storage
If you have less RAM storage then some of the apps will be stored on the hard disk which is much slower
When we want to work or understand complex things what can we do?
Create models , these models capture essential features of the original leaving out unnecessary detail.the process of creating simplified representation is known as abstraction/simplification.
What
What is abstraction /simplification
This the processes of transforming complex real world data into simplified easy to use models that captures essential features.
What is raster data (field data )
Raster data is grid based data (organized into rows and columns)consisting of equally sized cells or pixels, each with a value that corresponds to information ( such as colour, elevation or temperature).
Raster gives continuous data representation suitable for depicting phenomena that changes gradually across a landscape ( eg. elevation )
What is vector data .(object based data)
This represents geographic features using points, shapes, lines or polygons . Suited for geographic features with clear defined boundaries and locations.
Each feature can be linked to a distinct attribute (provides detailed description about said features).
What are some data sources for raster data .
Aerial photos
Satellite images
Scanned maps
What are some data sources for vector data
Field survey
Site investigations
Mapping, digitization from aerial photos
Interpretation of remote sensing data
Map digitization
True or false: no data set is exactly the same as reality but a higher resolution data comes very close
True
How are inexact data sets made exact ?
By approximation
True or false : many natural features have unclear / ambiguous boundaries.
True
What is approximation
This is when real world data up is represented in a simplified manner to facilitate analysis, visualization and storage.
True or false: a hotel an be represented by points or a polygon depending on scale .
True
When does one think about whether the data set will be raster /vector ?
The data collection /capture point .
Hy is satellite data much better suited to raster data .
?
Because satellite imagery consists of a grid of pixels with values
How can you make raster data vector?
This can be done through vectorization( which basically involves transforming pixel based images into geometric shapes , Ike points lines or polygons.) you start by reclassifying similar pixel values into distinct categories. Then polygonise,the soomth out borders and remove irrelevant small polygons
How is vectorization done?
Reclassify raster data ( group similar pixels into distinct categories.(eg. Pixels representing vegetation can be classified into forests, shrubs etc)
Polygonizationn convert contiguous ( pixels/features adjacent to each other) of the same class into vectors polygons
QGIS that has a vector to raster tool.
Remove small irrelevant polygons or smooth boundaries to better represent real world features.
How can you make vector data into raster?
Define raster parameters: resolution determination (cell size,(smaller cell=higher resolution)
Set spatial extent to cover area of interest.
Assign values to raster cells based vector attributes.
GIS tool can be used in softwares ( click “feature to raster” in ARCGIS in QGIS ( click “rasterization)
You may need to reclassify , resample the raster data set.
True or false: cells = pixel ( picture) , each pixel has a value and indicates the measurement of the area it cover .
True
True or false: the pixel in the grid reflects to some extend the real world location.
True
True or false: pixel size = resolution , the smaller the pixel size the higher the resolution.
True
When is coarse resolution appropriate
When taking the overview of something eg: topography
Example of a coarse and fine pixel size .
Grid2+ = 2m per pixel size =very fine
Grid50+ = 50m per pixel size (very coarse
True or false: if you can see variations within the image, like buildings ,cars,boats then the resolution is fine
True
How are different characteristics at the same location stored?
They are stored in multiple rasters
True or false: resolution should always be appropriate for the analysis required ( because to high resolution may provide unnecessary data , and too low of a resolution may cause data gaps
True
What is the equivalent of resolution in raster data set ?
Resolution = cell size
