Flashcards
GIS Flashcards
Cards in this deck (137)
- 1What are spatial data?Spatial data are a collection of measurements taken at specific locations. Data that are mappable (on a map, in a GIS)
- 2What is a map and what is its purpose?It is a form of communication which is a representation of reality. Uses colours, symbols to communicate information about location and relationships of locations
- 3What is distorted in the Gall-Peters projection?Stretching of the equator which draws your eye in to focus on those areas
- 4What is distorted in the Mercator projection?-Greenland, NA are shown larger and therefore appear to have more prominence
- 5What is a geographic information system?A system for capturing, storing, checking, integrating, manipulating, analyzing and displaying data which are spatially referenced to the earth
- 6What is the true shape of the earth?Oblate spheroid: A sphere which has compression at the poles, arising from centripetal force during rotation
- 7What are disadvantages to globes?-small scale, few details
-costly to reproduce or update
-difficult to carry around
-bulky to store - 8What is the main disadvantage to a 2D map?Distortion: you cannot make a 3D object fit on a 2D surface without distorting either area, shape, direction, or surface
- 9What are the types of class projections?1) Plane
2) Cylinder
3) Cone - 10What do the longitude and latitude lines of a planar projection look like?Longitude: Straight and equally spaced from centre
Latitude: Centric circles, equally spaces
(Bicycle wheel) - 11What do the longitude and latitude lines of a cylindrical projection look like?Longitude: Equal spacing: straight and parallel
Latitude: Straight but not always equally spaced - 12What do the longitude and latitude lines of a conical projection look like?Longitude: Straight lines diverging
Latitude: Circular, around the poles - 13What are the two cases of map projections?Tangent: the DS touches the RG along one line or one point
Secant: DS passes through the RG (>1 POI) - 14What is aspect?The position of the projection with respect to the reference globe (defines the latitude of origin)
- 15What would an oblique aspect projection be useful for visualizing?A single area not found at the poles or equator, such as North America
- 16What is a minimum error projection?Provides distortion errors for all properties at a lesser value than would be observed otherwise
- 17What does a conformal projection retain and distort?Preserves shape but not area
- 18What does an equivalent are preserve and distort?Preserves area
- 19What is a Robinson Projection?A compromise projection: a minimum error projection which distorts each category to a small degree
- 20What is the "unprojected projection" and why is it commonly used? Is it accurate?Assigns a grid system based on latitude and longitude with equal distance between lines. Popular due to ease of use with grid format
- 21What is the Fuller projection? Why is it accurate but not useful?The fuller projection is an unwrapping of the globe. Maintains shape and area, however direction is lost, thus it is useless for navigation, etc.
- 22What are graticules?In cartography, a network of lines representing the Earth's parallels of latitude and meridians of longitude.
- 23What is the UTM system? What does it conserve and distort? Why is it useful?Maintains shape and is based on a cylindrical, conformal projection. Easy to navigate and understand because distance is presented in metres, not degrees
- 24How does the UTM system work?Divides the globe longitudinally into 60 narrow zones with a central meridian in each zone. This acts to minimize distortion.
- 25What units are used in UTM coordinates?A UTM georeference consists of a zone number, a six-digit easting and seven-digit northing.
- 26What is the representative factor of a map?The ratio between the distance on the map and the corresponding distance on the ground (map distance: ground distance)
- 27What are three ways scale can be represented?1) Representative fraction
2) Verbal statement
3) Graphic/Scale bar - 28Which types of maps are more detailed? Which are more generalized?Large scale = detailed
Small Scale = generalized - 29What are the two components of spatial data?Location: describes where a thing is
Attribute: provides information about the thing - 30What is an object model?-Method for representing discrete, individual objects
-Space is represented as a collection of self contained objects
-Objects include lines, points, polygons: uses vector data - 31What is an example of an object model?Crimes: each crime is an object with a spatial location
We can includes attributes: type, cost, who responded
-generate spatial relationships with other crimes - 32What are field models?-considers that phenomena have spatially continuous attributes
-A value is possible at an infinite number of point locations of a surface
ex: temperature - 33What is a vector representation?-composed of points
-three or more lines can be joined to make an area
-Layers may be individual or combined - 34What is an area?An ordered set of point coordinates that represent a boundary, with the first and last being identical
- 35What is a raster image?-Composed of pixels with single values
-Can be combined to represent lines or areas
-Can make 3D surfaces when identity represents a Z - 36What can we use queries for?To access both spatial and attribute data to look for patterns, trends, and outliers
- 37What is a database?An approach to information organization in a computer environment. A common database model for GIS is relational (RDMS)
- 38What is topology?The science and mathematics of relationships (geometry)
- 39What does topological data store?-Associated with vector representations
-Stores information on spatial relationships or connectivity - 40What is topology used for in GIS?-Ensure that all polygons close and that all lines and networks are connected
- 41What is a buffer?A zone around a map feature measured in units of distance or time; useful for proximity analysis
- 42What is geoprocessing?-The generation of a new layer by performing an action/transformation on another layer followed by a query
- 43What are three important considerations when buffering with the wizard?1) Specified Distance
2) Distance from an attribute
3) Multiple rings - 44What is dissolving?Merging intersecting buffer zones into one single large zone
- 45In which situation would you want to dissolve a buffer?-When you are interested in total area or perimeter
- 46When would you want to refrain from dissolving the buffer?-You can find more information about individual locations
- 47What is a proximity analysis?A type of analysis in which geographic features are selected based on their distance from other features or cells
- 48How does proximity analysis differ from buffer analysis?Proximity analysis and buffer analysis can be similar, but proximity also includes "nearest place" or "shortest path"
- 49What is an intersection?An overlay method that has attribute data transfer
- 50What is a union?-Simply bringing two layers together
- 51What happens as a result of a clip?-Input feature will be reduced in size or shape based on what the output feature will be
- 52What does an intersect result in?Keeps only those features that are common in both layers: output type is based upon input layer
- 53What does an identity search result in?Identity keeps all the features of the first layer and those that overlap with the identity layer. Order matters.
- 54What are slivers? When may they resukt?-May result in spurious polygons (you have essentially created extra polygons you don't need)
-May result in spatial overlay when you have common boundaries - 55What is an equidistant projection? Name examples.Preserves distance between two points (Azimuthmal equidistant projection)
- 56What is an Azimuthal projection? Name an example?Preserves direction between two points (Lambert: confromal conic)
- 57What is Equivalent/Equal area (name an example)Preserves area (Molleweide, Albers =conic, Galls-Peter = cylindrical)
- 58What is a conformal projection? name an example.Preserves shape (Mercator, cylindrical)
- 59What is a raster?-Anything with a repeating pattern
-Can be any shape
-Space is tessellated - 60What types of data are raster data?-Remote sensing data
-Satellite data
-Modelling algorithms - 61What is remote sensing?Collecting data that is remotely sensed (ex: images, photo with a camera, satellite data, radar, sonar, etc)
- 62What is the difference between continuous and discrete rasters?Continuous: individual values represent something
Discrete raster: classed cell values that mean something (not a numerical value, a category). Pixels with the same number are in the same class - 63What tool do you use to convert a vector to a raster?The feature to raster tool
- 64What are some issues with using rasters to represent points, lines, or small areas?-Raster is less spatially accurate and does not display the location
-If the pixel size (output) is larger than the input, low resolution occurs - 65How much more data can a pixel half the size of another pixel store?4x the data can be stored by cutting the pixel size in half
- 66Why is raster data used?-Can be compressed and stored easily
-Allows for elimination of irrelevant information - 67Why should all raster sets in your worksheet have the same resolution?In order to be able to perform data analysis
- 68How do you query raster data?Using the raster calculator
- 69What are Boolean operators?And, Or, Not
- 70What does an output of 1 using a Boolean operator mean?That is the area of interest you were querying, a value of zero means that area is irrelevant
- 71What does a Boolean phrase of Xor mean?Values are present in the cells of one input rater or another input raster, but not both
- 72What are some limitations of raster?-You can only keep one part of information at a time
-Even with the highest resolution of data, you will still have sharp boundaries between classes - 73What is a network?-A system of linear features that has the appropriate attributes for the flow of objects
-topology based
-Attributes may include link impedance, turns, one-way streets, over/under passes - 74What type of information can be gained doing a network analysis?1) Network model
2) Shortest path
3) Traveling vendor
4) Location Allocation - 75What is an important component of network analysis?-Control mobility
-flow of goods, services, and informatiom - 76What is the structure of a netwoek?-Links: line segments connected to at least one other link
-Nodes: junctions of links, and also endpoints
-Valency: number of lines at each node - 77What information do we need in order to do shortest path analysis?-Direction
-This is usually defined by a single letter in an attribute table - 78Why may an incorrect map be useful when representing networks?If the incorrect map simplifies the system in a way which makes navigation easier (ex: the london underground tube)
- 79What is link impedance?-Cost of transversing a link
-Measured in distance or time - 80What is a turn? What is this a form of?-A turn is a transition from one street segment to another at a junction
-Turn impedance is the time is takes to complete a turn - 81What is the difference between shortest path and traveling vendor?Shortest path: shortest path from a specified origin through a set of destinations in a specified order
Traveling vendor: find the shortest tour from an origin through a set of destinations and back to the origin - 82What is an impedance matrix?Summary of the impedances from one path to another
-May have a symbol that depicts there is no direct connection - 83What does increasing the number of nodes increase in a shortest-path analysis?It increases the complexity of the matrix
- 84What are the two constraints ofhthe travelling vendor problem?1) The vendor must visit each of the selected stops only once
2) The vendor may start from any stop but must return to the original stop - 85What is a heuristically solved problem?Heuristics: algorithms designed to work quickly, and to come close to providing the best answer, while not guaranteeing that the best answer is found
- 86What is the complexity of the travelling vendor problem?(n-1)!/2
- 87Why are we not guaranteed the best solution for the travelling vendor probem?-Because there are too many possible routes to attempt to solve them all
-It stops reshuffling when it appears there is no more improvement - 88What is the vehicle routing problem?-Va-Variation of the TVP
-Given a fleet of vehicles and customers, an attempt to schedule vehicle routes and visits to customers in such a way that the total travel time is minimized - 89What are some additional constraints that may exist with the vehicle routing problem?-Time windows, vehicle capacity, dynamic conditions like traffic
- 90What is the closest facility analysis, and what types of situations is it useful for?-Closest facility finds the closest facility to any location or network
-Fire fighting, finding an atm, etc - 91What do location-allocation problems deal with?-Supply and demand
-minimizing travel
-maximizing profit - 92What are the three segments of GPS?1) Space segment: consists of 24 satellites and extras
2) User segment: receiver (often hand-held)
3) Control segment (five ground stations) act to correct locational errors from satellites - 93What are some characteristics of the space segment?-24 satellites plus redundancies
-20,000 km up from earth
-designed to provide maximum coverageof the earth - 94What are some characteristics of tthe control stations?-5 control stations
-provide checks regarding position of the satellite and speed
-Corrects any errors - 95How are distances measured using GPS?-Distances are measured according to the time needed for radio signals transmitted by satellites (space) to reach a receiver (user)
distance = travel time x speed of light - 96What will two satellites give you? 3? 4?2:2: give you two points
3: will give you intersection
4: will give you elevation - 97What is trilateration?Determining the absolute or relative distances of points using circles, spheres, or triangles
- 98What are some GPS applications?Precision farming, resource management, mapping and GIS, surveying, navigation, machine control
- 99What is GDOP?Geometric dilution of precision (GDOP)
-four satellites at close angles will have more error than those at low angles - 100What are some other sources of error associated with GPS?-Atmospheric propgation delays GPS signals as they pass through the atmosphere
-Satellite positions (GDOP)
-Clock drift
-Satellite ephemeris data - 101What is a service area? What is a service network?Service area: the region within a certain travelling distance or time of a site
Service networks: the streets within your defined distance or travel time - 102What are three types of impedance?1) Link impedance
2) Turn impedances
3) Stop and stop impedances - 103What are the four types of network analysis?1) Shortest path
2) Travelling vendor
3) Closest facility
4) Location-allocation - 104What is cartography?The art and science of making maps. Must include artistic input such as colour selection for symbols
Must include scientific data presented in the highest quality way possible - 105What are two classifications for mapping areal data?1) Chorochromatic: qualitative and nomial
2) Choropleth: quantitative and ordinal, interval, and ratio data (area+value) - 106What is the key to a successful map?Classification
- 107What are some rules about classification of data?-You must have exhaustive classes
-Classes should be mutually exclusive (no overlap, data is only found in one class)
-numerous enough to avoid sacrificing accuracy of data, but not so numerous as to impute greater accuracy than is warranted by the data - 108What are the key to a successful Choropleth map?Class intervals
- 109What is the purpose of data classification?1) Reduce observations into a manageable size
2) Identify groupings of observations
3) Reveal information otherwise obscured - 110How does fewer classes display the message?Fewer classes means a louder message
- 111How does more classes depict data?More information is present, but the message may become confused
- 112What are the three basic schemes for classifying attributes?1) Natural breaks
2) Quantile
3) Equal intervals - 113How does natural breaks (Jenks) classification work?-Classes are based on natural groupings inherent in the data
-minimizes within group variance, maximizes between group variance - 114How does equal interval classification work?-The range of attribute values is classified into equal-sized subranges
-we specify the number of classes, arcMap identifies where breaks should be - 115How does Quantile classification work?-Each class contains an equal number of features
-may lead to misleading results because similar features can be put in adjacent classes, or differing features into the same class - 116What are some advantages and disadvantages of the equal interval system?Advantages: easily understood, simple to compute, no gaps in legends
Disadvantages: does not consider distribution of the data, may produce classes with zero observations - 117What are some advantages and disadvantages of natural break (jenks)?Advantages: attempts to minimize class variance and maximize difference between classes
Disadvantages: complicated to compute, difficult to understand groupings, breaks may not be obvious, may miss natural clustering of data - 118What are some advantages and disadvantages of the Quantiles system?Advantages:
-produces an even looking map
-effectively masks outliers
-gives a sense of diversity even when there is little
Disadvantages:
-similar features can be places in adjacent classes
-features with widely different values can be put in the same class - 119What type of representation should you use for chloropleth data?Use derived data over absolute
- 120What is elevation generated from?-existing contour maps
-stero aerial photography
-satellite imagry
-laser flights - 121What is a DEM?DEM = digital elevation model
-a raster grid with elevation values - 122What do contour lines or isopleths connect?They connect points of equal interval
- 123What are contour intervals?The vertical distance between contours
- 124What type of analysis is deriving slope and aspect?Neighbourhood raster analysis
- 125What type of analysis is converting slope to % to deg?A local raster analysis
- 126Which DEM resolution would give you the best picture? USGS 30-m USGS 10-m LIDAR 1.83-mThe 1.83 m. The image will have more rows and columns and the pixels will be smaller meaning the resolution will be higher.
- 127What is aspect? In terms of GIs and in terms of a definition?It is a raster layer
-It is the direction of the slope (each cell has an azimuth value from 0-360 degrees)
-Flat areas = -1 - 128What is something to watch out for with aspect?Values near 0 and near 360 degrees are actually facing the same way
- 129What is hill shading? how is it depicted in GIS?-It simulates interactions between sunlight and the surface of the ground
-Value assigned between 0 and 255 - 130What four factors are needed to calculate hill shade?1) Surface slope
2) Surface aspect
3) Sun's azimuth
4) Sun's altitude - 131What is draping images?Why is it seful?It is taking a digital elevation model (DEM) and overlaying it on top of a satellite image
-Provides perspective, allows for rotation of scenes and changing of viewing angles - 132What is a TIN? What is an application of TINs?TIM = Triangular Irregular Network
-Vector-based, used to represent surface morphology through connecting verticies into triangles
-Allow for calculations of area/volume, more useful in small areas - 133What does LIDAR stand for? What is it?LIDAR = Light detection and ranging
-A new kind of data for terrain mapping
-data is collected as a high-resolution series of points - 134What is a point cloud?A collection of 3D elevation points including x,y,z and additional attributes like GPS time stamps
- 135What can LIDAR point clouds be used to generate?You can use LIDAR point clouds to generate extremely high-resolution DEMS
- 136When considering map design, should elements be arranged around the geometric centre or the optical centre?Objects should be arranged around the optical centre
- 137—
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- Flashcards on GIS Flashcards, created by Melanie Horne on 09/01/2016.
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