GEOG 281 Final Flashcards
What is GIS and how is it different from things such as google maps?
a method that utilizes specialized software to analyze spatial data, it is different because of its use of databases
What are the components of GIS?
people, data, procedures, hardware, and software
What are the distinguishing features of GIS?
use of spatially referenced data, graphical and attribute input and editing, selective spatial analysis tools, and map and report generation
What are the origins of GIS?
first GIS map - cave paintings of animal migration routes
first GIS analysis - John Snow 1854 Cholera map
what are the applications of GIS?
mature technologies (cartography), management and decision-making groups (urban planning), science and research activities
Why is GIS so important?
geography is part of our everyday world, every decision we face is influenced by geography, lots of government is based off of geography
How do we represent reality?
data models, a mathematical construct for representing geographic objects or surfaces as data
What are some basic spatial data models?
vector and raster
What are the advantages of vector?
more aesthetically pleasing, no data conversion required, accurate geographic location of data maintained, efficient coding of topography
What are the disadvantages of vector?
locations of each vertex need stored explicitly, must be converted into topological structure for analysis, algorithms are complex, continuous data is not represented properly, spatial analysis within polygons is impossible
what are the disadvantages of raster?
cell size determines data resolution, difficult to represent linear features depending on cell resolution, hard to process large datasets, more processing requirements, do not conform to high quality needs
what are the advantages of raster?
geographic location of each cell is implied, data analysis is easy and quick, suited for mathematical modeling, shows discrete and continuous data well, compatible with raster-based output devices
What is vector data composed of?
points, lines, polygons/area
How does raster data work?
makes use of pixels, each raster cell only contains one discrete value
what is a map?
a representation of a selection of material or abstract features on, or in relation to, the surface of the earth
What are the two broad categories of maps?
topographic map - a reference map tool, which shows many natural and cultural geographic features
thematic map - displays spatial pattern of a theme or species of attributes
what is map scale and how does it work?
the ratio between distances on the map and corresponding distances in the real world
large scale - shows a smaller region with greater detail
small scale - shows a larger region with less detail
how do we map the earth?
with geographic coordinate systems
what are map datums?
a mathematical formula that combines an ellipsoid and its geoid fit to surveyed control points
what are different ways we categorize map projections
distortion, shape, aspect
what are the different map projections by distortion
equivalence (area), equidistance (scale and distances), and conformity (angles and shapes)
what are the different map projections by shape
cylindrical (cylinder), conic (cone), azimuth or planar (plane)
what are the different map projections by aspect
normal (parallel), transverse (perpendicular), oblique (other)
which is latitude and which is longitude
latitude - horizontal
longitude - vertical
what is the difference between ellipsoid, geoid, and spheroid?
ellipsoid - a 3D, oval-like shape used to mathematically model earth
geoid - earth’s sea level shape, influenced by gravity
spheroid - a slightly squished sphere
what are some vector data structures?
spaghetti model, vertex dictionary, DIME, arc/node topological model
explain arc/node topological models
the mathematical model used to define spatial relationships in a GIS, point-line relationships
how is vector data created and managed?
input of spatial data, input of attribute data, then linking spatial and attribute data, saved in flat files, hierarchical, or relational
explain querying (vector)
the selective display and retrieval of information from a database
explain measurement (vector)
measurement of straight-line distance between x and y or the area of a section of land
explain buffering (vector)
summarizes distance or proximity by creating distance buffers around selected features
explain overlay (vector)
a series of operations performed on spatial data in different layers, which produces new layers of data
what is network analysis in vector?
use topological relationships to represent and analyze flows along a set of interconnected paths
Which two ways does vector model surfaces?
sampling - sample field variations by recording its value at a limited number of locations
inverse distance weighting - estimates interpolated cell values by averaging values of sample data points in the neighborhood of each processing cell
how do you create a raster?
choose grid resolution, set data type, overly grid over study area, assign attribute code to each grid cell, repeat process for each map layer
what are different methods of encoding data values?
presence/absence, centroid of cell, dominant type, percent occurrence
how do map layers work in raster?
only one attribute value may be assigned to each cell, objects with several attributes are represented with a number of raster layers
how does raster data storage work?
band interleaved by line (BIL) - rows follow each other for each characteristic
band interleaved by pixel (BIP) - all values for a pixel grouped together
band sequential (BSQ) - stores each characteristic in a separate file
what is run length encoding? (raster)
a data compression method, if data is 1 1 1 3 3 4 4 4 5 it would be compressed into 3 1 2 3 3 4 1 5
what are pros and cons of BIL (raster)?
pro - efficient access, compact storage
con - slower processing, not good for visualization
what are pros and cons of BIP (raster)?
pro - good for focusing on multiple area characteristics
con - bad if you want to remove or add layers
what are pros and cons of BSQ (raster)?
pro - compression and good for focusing on one characteristic
what are local operations (raster)?
reclassification, overlay analysis
what are focal operations (raster)?
filtering, slope, and aspect
what are zonal operations (raster)?
identification, areas, perimeter, distance from boundary, shape
what are global operations (raster)?
distances, buffer zones, viewsheds, least cost pathways
what is the importance of data?
data determines what you can analyze, where you analysis focuses on, types of analysis, and quality of your analysis
what are different data sources?
primary raster (digital remote sensing, digital aerial photos)
primary vector (GPS measurements, survey measurements), secondary raster (scanned maps, DEMS), secondary vector (topographic surveys, toponymy data sets from atlases)
what are errors, accuracy, and precision?
errors - distort measurements by small amounts
accuracy - refers to the amount of distortion from the true value
precision - refers to the variation among repeated measurements
what are some different issues with data sources?
users may be unaware of available data, difficult to determine if data are suitable for users applications, format issues (scale, projection, translation)
what are some different technology issues
integration of GIS into database management systems, competing claims from software vendors, each product has its own strengths and weaknesses, and benchmarking (evaluate software using own data)
what is the connection between spatial analysis and GIS?
spatial analysis is a key function of GIS, GIS provides the tools to perform spatial analysis, allowing users to examine geographic patterns, relationships, and trends in the data
what are descriptive summaries?
attempt to summarize useful properties of data sets in one or more statistics (often mean or average)
what is pattern detection and how does it work?
patterns can be identified as clustered, dispersed, or random
can measure looking at physical location and geometric patterns of features or looking at geographic patterns in the attribute data of features
what is GIS-based modeling?
spatial models, attempt to represent variation over earth’s surface, it manipulates geographic information in multiple stages
what is multicriteria decision evaluation?
involves overlaying thematic layers and finding locations that encompass all desired criteria, two techniques:
boolean intersection - uses logical operators to find combinations of layers
weighted linear combination (WLC) - asses the suitability of locations by weighting and combining maps
what is presence/absence encoding?
a single feature is identified as occurring in a cell, no matter how much space it occupies
what is centroid-of-cell encoding?
presence of an entity is recorded only if a portion of it occurs directly at the central point of each cell
what is dominant type encoding?
encodes the presence of an entity if it occupies more than 50% of the cell
what is percent occurrence encoding?
3 types of land use occur in a cell, then each type would be represented as the percentage of the cell it occupies
