Midterm one Flashcards
(75 cards)
1
Q
What is In Situ Data Collection? What is it good for?
A
-Someone is collecting data at some point in time, geographically in person
-good for precision in small areas, surveying, and accuracy
2
Q
What are examples of In Situ Data Collection?
A
GLCTS
1. Gps; global positioning system
2. Land surveying; plane table –> field measurements are observed and plotted at the same time
- Census; systematic collection of information about all the members of a given population every 5 years
- Total station
–> uses a theodolite, measures distance electronically with a laser level to the horizontal plane but takes into account both vertictal and horizontal controls (sidewalk) - Smart station; total station with a GPS
–> triangulate and reset position when there is obstacles in the signal. Uses GPS enabled sedia rod
3
Q
What is the census that maps all of Windsor-Essex County?
A
United Way
4
Q
What is Digitizing data in GIS? What does the process look like on a digitizer table?
A
- Digitizing in GIS is the process of converting geographic data from hardcopy/scanned image into vector data by tracing the features as points, lines, or polygons
- Take digitizer tablet with wire mesh under surface –> the puck/cursor moves over the tablet surface –> puck has numbers on it that sends positional info from the wire mesh into the computer software
5
Q
What is Digitizing data in GIS? What does the process look like on a digitizer table?
A
- Digitizing in GIS is the process of converting geographic data from hardcopy/scanned image into vector data by tracing the features as points, lines, or polygons
- Take digitizer tablet with wire mesh under surface –> the puck/cursor moves over the tablet surface –> puck has numbers on it that sends positional info from the wire mesh into the computer software
6
Q
What is the problem with scanning digitization of data?
A
TEEIO
1. Tolerance is low to background noise
2. Editing required
3. Export to GIS may not be possible
4. Irrelevant info
5. Optical distortions
7
Q
What are the two types of digitizing data in GIS?
A
- Scanning; converts an analogue source into a digital raster format. beam of reflective light is moved over the paper document to form an image
- Automatic Line following
8
Q
What is the remote sensing process?
A
SDDI
1. Statement of the problem; hypothesis
- Data collection; In Situ, Collateral Data, Remote Sensing
- Data to information conversion; analog image processing, digital image processing, hypothesis testing
- Information presentation; image metadata, accuracy assessment, analog and digital, statistics and graphs
9
Q
What is remote sensing?
A
the science of awuiring information about the earths surface without actually being in contact with it. Done by sensing and recording reflected/emitted energy and processing then analyzing the info
10
Q
What are the two types of Remote sensing data collection methods?
A
- Passive; energy leading to radiation received from an external source
- Active; energy generated from within the sensor system is beamed outward, and the fraction returned is measured
11
Q
What are the four types of resolution?
A
TRSS
1. Temporal resolution; dates and times of data capture from satellite
- Radiometric resolution; sensitivity of the sensor
- Spectral resolution: number and size of specific wavelength intervals based on the electromagnetic spectrum –> infrared
- Spatial resolution –> measure of the smallest angular or linear separation between two objects that can be resolved by remote sensing. every satellite is different
12
Q
What is a pixel
A
the 2D picture element that is the smallest non divisible element of the digital image
13
Q
What are some examples of remote sensing
A
RLLU QNM
1. RADAR; radio detection and signalling
-Active sensor, long wavelength, detect terrain roughness
2.LandSat; land + satellite
-multi spectral scanner, thematic mapper and an enhanced thematic mapper; inexpensive; high spatial resolution
- LiDAR; light detection and laser altimetry
-collect dense and accurate elevation levels;3D terrain; uses laser light pulses - Unmanned aerial vehicles; drones
-flying robot that can be controlled autonomously through software controlled flight plans in their embedded systems; sensors and GPS - QuickBird; satellite image with aerial photo quality
- NOAA-AVHRR; advanced high resolution radiometer
- MODIS; moderate resolution imaging spectroradiometer
-two satellite sensors, terra (morning) and Aqua (afternoon)
14
Q
What is a Geo portal?
A
A type of web portal used to find and access geographical information (geospatial information) and associated geographic services via the internet; essential for GIS and SDI
15
Q
What is cartography?
A
Chartis (map) Graphein (write)
-The science and oractice of making representations of the earth on a 2D flat surface or a 3D globe
-The discipline dealing with the conception, production, dissemination, and study of maps
-the whole process of mapping
16
Q
What are some Cartographic milestones
A
- Cave drawings etched onto stones were first maps; spherical
- Ptolemys world map (1482) showed lat and long
- 15th -16th cent was age of exploration
- 1440 was the printing press
- 16th cent the Atlus was created
- 17th-19th century map making became more accurate due to surveying techniques
- 1960-present; computer mapping and spatial technologies
17
Q
What is the Cartographic process?
A
effectively and efficiently communicate spatial information in a map based framework
- PURPOSE How general vs specific/scientific should the map/info be? what is the distribution?
- DATA COLLECTION; local measurements? global?
- CARTOGRAPHIC PRINCIPLES (design)
- INTERPRETATION
- CRITIQUE
18
Q
What are some map features?
A
- layout, title, topography, figure, north arrow, scale bar, grid, metadata/sources, labels
19
Q
What are the different symbols when Mapping point data?
A
PGSS
1.Proportional symbols; each map symbol is proportial in size based on an observation
- Graduated symbols (colour)
- Simple symbols
- Standardized symbols; government mandated USGS
20
Q
What are some measurement levels?
A
Numeric; interval, ratios
Nominal; discrete, independent entities
Ordinal; area
21
Q
What are the different lines when mapping (vector?) data
A
SIG
1. Simple lines
2. Graduated/proportional lines
3. Isolines (Isarithmic mapping); using lines to create a smooth and continious surface
22
Q
What are the types of Isarithmic mapping
A
IIT
1. Isometric maps; based on true data control points to generate a statistical surface of a particular geographic location
- Isopleth Maps: based on conceptional data points to generate a statistical surface of a particular geographic location
- Topographic and bathymetry maps; Lines set at equal distances that show levels of elevation or depression of the earths surface
23
Q
What is choropleth mapping?
A
The mapping of spatial data within a constrained boundary
-consider factors related to geographical areas ex how many dogs live here? why? is it related to population?
24
Q
What is georeferencing
A
- taking something 3D and concert into 2D space/slat surface
- the ability to locate earth based features or objects accurately and precisely in a geographic space
- assigns locations in 3D to points on a spheroid/ellipsoid
25
What is Geodesy?
the study of the shape and size of the earth and location of points upon the earths surface
26
What is an ellipsoid?
-geoid (basic earth shape based on sea level)
-rotational factor
-compressed
-Good for precision of location
- Takes into account the earths irregular shape
-Equator and pole radiuses are separated (slight differences in distances)
-North and south poles are flatter
-Usually used as reference surface for horizontal measurements (latitude and longitude)
27
Geogeist theory with how earth models came about
-began with complex earth
-take away surface topography shape
-left with basic shape based on sea level (geoid)
-Consider earths rotation on an axis (a ellipsoid)
-simplify more to get a spheroid
28
What is a geoid?
-irregular shape (unevenly distributed earth)
-basic shape based on sea level
-Differences in the density of earth caused variation in gravitational strength causing regions to dip below or above the reference ellipsoid.
29
What is a spheroid?
-similar volume to the ellipse
-not as compatible as ellipsoid is to the geoid
-makes distance, direction, and area easier
30
History of Geodesy
- Pythagoras (6th cent BCE) and aristotle (300-322BCE) belived that the earth was a sphere
-Eratosthenes (376-194BCE) was the first to mathematically calculate the circumference of the equation
-By the 18th century an imperfect shaped earth
-Newton, Huygens, French academy, and sailors believed earth was oblate spheroid
31
What is an oblate spheroid? how can its qualities be modelled
earth was flatter at poles but bulged at equator
modelled with reference ellipsoid
32
What is a datum
-A reference or foundation surface against which accurate position measurements are made, a datum identifies “zero” on a measurement scale
-Spatial reference system that describes the shape and size of the earth and establishes an origin for coordinate systems
33
what are two main types of datums
LOCAL (geodetic) and GLOBAL (geocentric)
34
What are Vertical datums?
Is a network of spatially distributed points on earth with known heights either above or below sea level
-National geodetic vertical datum (1929)
-National geodetic veritcal datum (1988)
35
What do vertical datums establish?
Establish: Elevation: digital elevation model, digital surface model, digital terrain model, Bathymetry; seafloor terrain
36
What is a Horizontal Datum
-Collection of points on the earth that have been identified by their precise N/S location (latitude) and E/W location (longitude)
-Surveying of earth and positions on the ground are marked with a brass disk
-Year is the DATUM, the foundation peace
-North American datum 1927 (NAD27)
-North American datum 1983 (NAD83)
37
What are positional errors in datums ?
-There is a cycle of percise location serveys and then constructing coordinate lines based on it every few years. Casues a shift in data points
- important in large scale mapping applications (local scales) as these discrepancies will be much larger than any projection induced error
38
What is a Coordinate system?
A coordinate system is a way to describe a spatial feature/entity relative to a center
-What are coordinates: ways to reference location on map
39
What are the three base coordinate syste,s
1.Geocentric coordinate system
2.The spherical or geographic coordinate system
3. Cartesian coordinate system
40
How can lat and long be measured?
1.decimal/degrees
2.degrees/minutes/seconds
-Represents a world ellipsoid
41
What is Universal Transverse Mercator (UTM)
-Is a grid system that works by dividing the world into a series of zones, and then determining the x,y coordinate for a location in that zone
-Determine zone of intrest (ex 17N) then determine position with easting (6 digit) and northings (7 digit)
-projected coordinate system
-good for large scale
42
What is State Plane coordinate system?
-Cartesian grid based system (like UTM) Created in the 1930s. Used for US city and county data mainly
-Zones are formed following state and county boundaries. Every state is split between north and south while UTM splits the world, referenced in feet
43
What is a way of identifying location that is not a coordinate system?
-Postal codes
-First 3 digits = forward sortation area, Last 3 digit= local delivery unit
-Postal code conversion file= coordinates
44
coordinate vs datum vs projection?
-Coordinates the number
-Datum is the year measurements taken
-projection is then the distortion
45
What are Map projections ?
-Used to transfer the spherical earth (3D) onto a 2D surface, Allows for the systematic arrangement of parallels and meridians on a flat surface representing the geographic coordinate system (ex lat and long)
- introduce some level of distortion (bc flattening image)
46
What do you want to maintain when projecting?
1. Distance (maintains equidistance relationships so distance from centre is the same no matter what direction) = equidistance
2. Area (areas have proportional relationships to their corresponding features on the earth) = equal area
3.Direction (maintained when angles are portrayed correctly in any direction) = azimuthal
4.Conformity/shape (maintains angles, so no N/s, E/W lines intersect at 90 degrees, but at expense of distance = conformal)
47
What are Conic projection? What is one main type? ?? CHECK SLIDE
-Distances at center are true but the distortion in other properties increases as you move away from the center point.
- Area is distorted
-Distance is very distorted towards bottom of image
-Scale is for the most part preserved
Used in the United States and other large countries with larger east west than north south extent
48
What are Cylindrical projection properties?
-Continuous picture of the earth, Countries near the equator in true relative positions
-Distance increases between countries located toward the top and bottom of image. View at the poles is very distorted.
-Area for the most part is preserved
-Mercator works at local and global near the equator but the farther you go it is not very good for a local projection
49
What is an Azimuthal projection ?
-Flat paper on globe and wherever the paper touches the globe is the center point and where accuracy is conserved
-Part of earth is visible; not the entire globe just partial; maybe more hemisphere or continent. View is half of globe or less
-Distortion occurs at all four edges.
-Distance is for the most part preserved; good if distance is variable of study
- mainly used for polar research
50
What is the Tissot indicatrix?
-Ways to understand distortion of projections
-geometric deformation indicator that is an infinitely small circle on the surface of the earth projected as a small ellipse on a map projection plane. It helps depict distortions (areal, linear, angular)
51
What is one main type of conic projection?
-(Albers equal area)
-Scale and distance are distorted north to south but maintained west to east
-Areas are proportional and the directions are true
52
What is Geographic entity
real features found on the earth's surface
53
what is a Geographic object/feature
real features that have been transformed and represented in a digital world Digital objects and their associated attributes and values represent geographic entities
54
what are the different types of geographic features?
PAL
Points (fire hydrant, trees): aka nodes, labels
Area (census areas, land use): aka arcs (points with lines from front point to end point), polygons (closed figure). A closed string of coordinate points that are connected by nodes and vertices and arcs --> sized and perimeter properties
Lines (roads, rivers): aka arcs, polylines. A string of coordinate points that are connected by nodes (the start points and end) and vertices and arcs
X Y will say HOW the points were derived
55
What are two problems that arise when we simplify the real world into 2-d
1. Determining discrete vs continuous features
2.World is constantly changing (ie, urban sprawl), therefore so do entities
56
How do we create and represent geographic entities/features within GIS?
1. Vector (point, line, area (polygon)); discrete method of data created with vertices, nodes, arcs --> stored as topological tables
2. RASTER (grid, pixels); Continuous
- assign different properties to each cell on the grid
- dont have signitfigent attribute table, if they do then it is based on the pixel value
-based on a grid -->columns and rows to create pixels
57
What is a vector data model?
A vector data model uses precise cartesian (ie. Digitizer)/geographic (ie. GPS)coordinates to store the location of a geographic entity
58
What are some Vector scale considerations
- Scale of the map display often indicates whether a feature is displayed as an area or as a point --> It is also wise to have all your layers using a similar scale
1. Large scale= more detail
2. Small scale= less detail
59
what are the two categories of vector data
1. Non- topological
2. Topological (NOT TOPOGRAPHY) geometric relationship that exist between entities located it space. It can be thought of as the study of how entities are organized relative to one another, whether they are adjacent; connected; or contained; Helps to detect errors in spatial data
60
What is the difference between Adjacency, Contained, Connected vector data?
Adjacency: the information about the neighbourhoods of different entities
Contained: the information about entities that enclose other spatial features
Connected: the information about the links between entities
61
How do we create vector files with topology
-Identify entity
-Know its going to become object
-Either place map on digitizer and trace
OR interacting digitizing
62
What are characteristics of topological vector structure data
1.Computer will recognizse start nodes, vertices potentially, and the arcs
2.Computers will make polygons, tell you which ones interact, the number of nodes and the arcs etc.
63
What are characteristics of non topological vector structure data?
-No tables
-Cant shift node/boundary and expect all the data to shift with it; doesn't have framework
-Over and undershoot cannot be fixed without topology; cant do things automatically like connect nodes
64
What is Raster Data Model? how is it represented?
- Used to describe and depict spatial entities that are continuous across a landscape
- Raster data are representing by an array/grid of cells in rows and columns
- each cell contains a value that describes the phenomena being examined (a measurement or description). cells are usually called picture elements (pixels)
65
What are the two stages to represent a map in raster format ?
1. cell size
-refers to x and y dimension of each pixel
-important because the raster layer has one value associated with each pixel --> only one type of land can be represented in each cell
2. cell value
-unique nominal, ordinal, or interval/ratio scaled value associated with each type
66
What is Raster Georeferencing?
- raster data must be georeferenced to relate them with other spatial datasets
-referenced using a coordinate system that is related to the number of rows and columns in the layer
- the georeferenced values can be interpolated within individual pixels
67
What is the structure of Raster data
- there are many but some broad groupings are:
CRSQ
1. Chain coding
2. Run-length encoding/block coding
3. Simple rasters
4. Quadtrees
68
What is Raster run length encoding/ block coding
-reduces data volume on a row by row basis
-stores a single value where there are a number of cells of a given type in a group, rather than sorting a value for each individual cell
-block coding: extends run length encoding approach to 2 dimensions by uitilizing groups of square blocks to store data
69
Chain coding
- reduction is based on the boundary of the entity/feature
-the boundary in this case is defined as the sequence of unit cells starting from and returning to a given origin
-the direction of travel around the boundary is usually given a number or letter system
70
How do you convert vector to grid ?
Start with vector data set containing polygons with associated attributes
a grid with the desired cell size is superimposed. The polygons which contain the centres of each of these grid cells are then determined
the values of the grid cells become the values of the attributes of the polygons which contain them
71
How do you convert grid to vector?
Start with gridded satellite classification with class numbers contained each grid cell
borders between differing class numbers are located
polygons are then generated for each contiguous area by storing the x, y coordinates of the points along these borders
72
What is the difference between rester and vector data volumes?
-Rester is larger
-Vector data sets have much smaller data especially for simple geographical entities
73
What is the difference between rester and vector relationship representation?
-rastr can be done with only quadtrees
-vector is good for topological questions (adjacency, connectivity, and containment)
74
What is the difference between rester and vector generality?
-raster scale increases which leads to "blocky" images creates problems if resolution is high
-vector handles scale and rotational changes better because entities are stored as precise coordinates
75
What is the difference between rester and vector analytical capability?
-raster models are better at
1. surface modelling and interpolation
2. analysis of continuous and complex data sets
-vector models are better at
1. analysis involving discrete spatial entities
2. simple overlays and geometric operations
