Final Exam Flashcards
What is the difference between Spatial and Attribute data?
The main difference between attribute data and spatial data is that the attribute data describes the characteristics of a geographical feature while spatial data describes the absolute and relative location of geographic features.
Explain GIS. What makes it unique?
(GIS) is a system that creates, manages, analyzes, and maps all types of data. GIS connects data to a map, integrating location data (where things are) with all types of descriptive information (what things are like there). This relational database is unique and crucial to the making GIS what it is.
What is a Vector data model? What are the main types of data?
A representation of the world using points, lines, and polygons. Vector models are useful for storing data that has discrete boundaries, such as country borders, land parcels, and streets.
What is Raster Resolution?
The spatial resolution of a raster refers to the size of the cells in a raster dataset and the ratio of screen pixels to image pixels at the current map scale.
The size of a cell (generally measured in meters (30m resolution = 30x30 metre cell size)
What are the 3 different Scale Calculations? (hint: triangle)
Scale = Ground Distance / Map Distance
Ground Distance = Map Distance * Scale
Map Distance = Ground Distance / Scale
How do you calculate Coordinates? (Degree Min Sec -> Decimal Degrees)
e.g. (49º 28’ 51”)
51”/60 =0.85’
28’+.85 = 28.85
28.85/60 = 0.4808
Answer = 49.4808º
How do you calculate Coordinates? (Decimal Degrees -> Degree Min Sec)
e.g. 11.3248º
0.3248 x 60 = 19.488
.488 x 60 = 29.208
Answer = 11º 19’ 29” E
What is the difference between large scale and small scale maps? (which is larger?)
Large scale maps show a smaller amount of area with a greater amount of detail. The geographic extent shown on a large scale map is small.
Small scale maps show a larger geographic area with few details on them. Small scale maps are used to show the extent of an entire country, region, or continent. (small scale is Larger)
What is a Geoid
The geoid is the shape that the ocean surface would take under the influence of the gravity of Earth, including gravitational attraction and Earth’s rotation, if other influences such as winds and tides were absent.
Geoid is an interpolated surface
based on gravity.
What is an Ellipsoid?
A mathematical model that smooths the irregular shape of the geoid.
The squished shape is due to the earth’s gravitation and rotation.
▷ The most accurate global ellipsoid is the World Geodetic System (WGS 84)
What is a Datum? why are they useful?
Use information about the earth from ellipsoids and geoids.
• Provides a starting point (origin) for mapping
• Use a mathematical model to fit the coordinate system (Lat / Long) to the surface of the earth.
What is a cylindrical Projection?
Cylindrical projections is like wrapping a cylinder around the earth.
Longitude = equal spacing; straight and parallel
Latitude = straight, but not always equally spaced.
What is a conic projection?
Conic projection is like wrapping a cone of paper around a portion of the earth.
Longitude = straight line diverging Latitude = circular, around the poles
What is a Planar Projection?
Planar projections like a bicycle wheel Longitude = straight equally spaces; radiate from centre
Latitude = concentric circles, equally spaced.
What is a developable surface? (what are the three types?)
Developable surface [map projections] is a geometric shape such as a cone, cylinder, or plane that can be flattened without being distorted. Many map projections are classified in terms of these shapes.
What is the CASE of the Projection?
The areas that touches the globe and has the least amount of distortion in the projection. (different for every type of projection)
What aspects can projections have?
The aspect describes how the developable surface is placed relative to the globe: it may be normal (such that the surface’s axis of symmetry coincides with the Earth’s axis), transverse (at right angles to the Earth’s axis) or oblique (any angle in between). “The aspect of the map projection refers to the orientation of the developable surface relative to the reference globe.”
What are the four types of projections? What do they preserve?
▷ Angles (Conformal)
▷ Area (Equivalent)
▷ Distance (Equidistant)
▷ Direction (Azimuthal)
What is an Attribute Join?
Attribute joins connect data in tables
using a common field. Joins can be permanent or temporary.
What is a Spatial Join?
Used when you want to create a join based on the location of features in space. generally done with overlapping layers.
Tables do not need to contain a common field.
What are spatial queries?
Spatial queries are queries in a spatial database that can be answered on the basis of geometric information only, i.e., the spatial position and extent of the objects involved.
They are based on topological relationships
▷ The spatial features themselves (not attributes) are used as part of your query
What is Topology with regards to GIS? Why is it important?
Topology is what sets GIS it apart from graphic and CAD software. (direction, what’s within/outside of an area) Topology expresses the spatial relationships between connecting or adjacent vector features (points, polylines and polygons) in a GIS.
Topology is also associated with Vector data
▷ A topological data model explicitly stores information on spatial relationships or connectivity.
▷ Topology used to make sure that all polygons close and that lines in networks are connected
What are Attribute Queries?
Attribute queries – selects based on conditions (for example, find single people with high income)
Essentially it selects a subset of the data.
e.g.
▷ Select crimes that involve thefts
crime type = theft
▷ Select crimes that happened after lunchtime time > 12
What operators are used with Attribute queries?
One attribute:
=, >=, <=, >, <
Multiple attributes need a connector:
▷ AND = both expressions must be true
▷ OR = either expression must be true
▷ NOT = 1st expression is true, 2nd is not true
What is a Boolean Operator?
In computer science, a Boolean is a logical data type that can have only the values true or false. Something either IS or IS NOT a
(1 = yes / 0 = no)
What is Spatial Proximity?
A type of analysis in which geographic features (points, lines, polygons, or raster cells) are selected
based on their distance from other features or cells.
What is a Raster Calculator? How can it be used?
The Raster Calculator lets you perform mathematical calculations using operators and functions, set up selection queries, or type in Map Algebra syntax. Inputs can be raster datasets or raster layers, coverages, shapefiles, tables, constants, and numbers.
What are Buffers? What are the different types?
A zone around a feature measured in units of distance or time. A buffer is useful for proximity analysis.
Buffers can exist around Points/Lines/Polygons and can surround the feature, be on one side or the other. They can be rounded and can be dissolved or undissolved.
How can Buffers be used?
A buffer analysis can be performed. This is a determination zone around a geographic feature containing locations that are within a specified distance of that feature, the buffer zone, and how they interact with that buffer zone.
What is the famous first example of using Proximity analysis to solve a problem?
Dr. John Snow, England (1850’s)
▷ Using a map to demonstrate
the spatial relationship between cholera cases and a particular water pump.
What is an Intersect?
Geoprocessing tool that finds overlaps between layers
▷ Keeps attributes from all input layers
▷ Can also be used to check for overlaps within the same layer
What is the output of an intersect? when would you use one?
Intersect keeps only those features that overlap
▷ Output type is based upon input layers
▷ If the inputs have different geometry types (that is, line on polygon, point on line, etc), the Output Feature Class geometry type will default to be the same as the Input Feature geometry type with the lowest dimension geometry.
e.g. Where does caribou habitat
intersect with heavy human use?
What is a Union?
Total area of both objects. The Union tool creates a new coverage by overlaying two polygon coverages. The Output Coverage contains the combined polygons and attributes of both coverages. Only polygon coverages can be combined using Union.
e.g. What area of parcels are within the
floodplain zone?
What is an Erase?
Geoprocessing tool that removes any areas of overlap between input layers.
Only locations in the input but not in the erase layer remain.
e.g. buffer around drinking fountains in neighbourhoods (erase to find areas not with a certain range)
What are Sliver Polygons? How can you get rid of them?
Long, skinny, irregular polygons, created when you perform an overlay (two different coastlines for instance), these polygons will throw off your results (adding to total area). You can get rid of them by merging them with adjacent polygons, also performing an erase by polygon size.
Truth & Reconciliation Lecture Points
Maps played a role in colonization, they can control the land, divide it, controlled the naming of places. Many of these maps still control how we see the world. “Decolonizing the map requires a recentering of indigenous geographical knowledge”
What can we do? Reconsider how we classify our maps / include territorial acknowledgement / Pay attention to names / Step Back, indigenous-led mapping.
What is a discrete raster?
Limited number of possible values ▷ Pixels with same value = same class ▷ Larger cell value does not mean more valuable ▷ Similar to polygons ▷ e.g. soil class, vegetation class, .
What is a Continuous Raster?
Unlimited number of possible cell values
▷ Larger cell value = higher value
▷ Same value does not mean it is in the same class – there are no classes
▷ Usually called a ‘surface‘
▷ e.g. elevation, precipitation
Why would you compress a Raster?
The primary benefit of compressing your data is to reduce the size of the file to help save disk space. This process groups like values together (counts numbers of cells and groups them)
