GIS (Geographic Information Systems) Paper Exam 1
Thematic rasters
- Contain quantities that represent map data such as land use or rainfall - May be continuous or discrete
Image Rasters
- Contain satellite or air photo data - Generally represent brightness - Usually continuous
Map Scale in action
- a small scale map shows a larger area (large denominator gives smaller fraction) - a large scale map shows a smaller area (small denominator gives a larger fraction)
What is the Modifiable Areal Unit Problem? (MAUP)
-Arbitrary aggregation units like states or counties may influence values -Number of farms in state is affected by size of state -Number of vacant houses in state is affected by population of state -Maps reflect the influence rather than the data being mapped
what is the RGB color model
-Based on mixtures of red, green, and blue primary light -Each primary color brightness is indicated on a scale of 0 (black) to 255 (bright) -Each RGB triplet represents a different color
What is the Jenks Natural Breaks classification?
-Exploits natural gaps in the data -Good for unevenly distributed or skewed data -Default method that works well for most data sets
What is a map projection?
-It is the conversion of a 3D map to 2D -It starts with a defined GCS and applies a set of mathematical formulas that covert the coordinates
give an example of a discrete raster:
-Land use -Precipitation -Ocean depth
How should you balance/align your map?
-Place elements in ordered columns rather than a haphazard arrangement -Align edges of boxes and frames exactly using guides and snapping -Balance your elements, reduce too much "empty space"
continuous raster data
-Represent a measurement that occurs everywhere. -Thousands or millions of potential values. -Few adjacent cells have same values. -Values may change rapidly from cell to cell.
discrete raster data
-Represent objects such as roads or land use polygons. -Take on relatively few values. -Adjacent cells often have same values. -Values may change abruptly at boundaries.
Stretching
-Stretching reallocates a smaller portion of the raster values to the 256 shades of the color scheme -Improves brightness and contrast -There are many types, such as min-max or standard deviation stretches
What are a few things you can map?
-Symbols -Graduated color polygons -Base layer with information
give an example of a variable that should be normalized by population on a map of all states?
-average annual snowfall -home vacancy rates -number of crimes reported
How do you convert to decimal degrees?
-divide the seconds by 3600 -divide minutes by 60 -add the degrees + minutes + secons
Digital vs. original scale
-original scale of the map does impact the precision and accuracy of the data - you should not display or analyze data at scales very different from the original source data
What is a historical reason why our modern maps look the way they do today?
-possibility that map makers were from the north
What goes into determining the objective of a map?
-purpose of the map -audience -medium (on a screen, paper)
What are a few things you should think about when choosing your colors?
-respecting color psychology -natural tones typically look better -use bold colors sparingly for emphasis -mimic natural phenomena -make ramps easily understandable -emphasis can be applied with color, size and thickness
What is a challenge that map projections must overcome?
-shape -area -direction -distance Projections can fix some of these but not all
What is Datum?
-uses a specific spheroid and translation to achieve the best possible fit between the earth geoid and the mapping spheroid
When would you use equal interval over jenks?
-when attempting to produce equal sized classes
What are three benefits of classifying data?
1) Divides data values in class ranges, each with its own symbol 2) Can be used as a data exploration tool 3) Different classification methods are available
If you measured 10 cm on the map, how many centimeters on the ground?
1/100,000 x 10/x = 1,000,000 cm
A 50 m long swimming pool measures 2 cm on a large scale map. What is the scale of the map
1:2500
Why would a pattern or color ramp be useful in many cases?
8% of the world has colorblindness
What type of data is "vegetation type"?
Categorical
What map preserves shape?
Conformal Projection -should be used when a map's main purpose involves showing accurate directions, measuring angles, or representing freatures ex: navigation charts, weather maps, civil engineering maps
In general, which type of projection would preserve direction?
Cylindrical
What is an "on the fly" projection?
Data that is stored in different coordinate systems can be drawn together
A shapefile has an Unknown coordinate system, but a file on the web says the coordinate system is UTM Zone 13 NAD 1983. What is the next step?
Define the Projection of the shapefile to UTM Zone 13 NAD 1983
What is the difference between discrete and continuous data sets?
Discrete are objects with specific locations or boundaries, continuous represent quantities that may be measured anywhere on earth
What map preserves area?
Equal Area Projection -the size of the map is true proportion to it's size on earth example: land use maps, GDP by country
What is logical consistency?
Evaluates whether a data model accurately represents the real-world relationships between features, such as do 2 streets intersect?
Attribute tables
Features are linked to tables containing information about the spacial objects; the map object and the table data are connected by a unique integer
Categorical Data
Features belong to categories -rock type, volcano type, highway class, or land cover class. Category names may be text or numeric
What does GIS stand for?
Geographic (coordinate), Information (table attached to each dot; attributes); System (hardware/software)
If a data set's features have x coordinates between -180 and +180, what is the coordinate system likely to be?
Geographic Coordinate System
If someone is using their smart phone to map a trail and they correctly enter the name of the trail but are getting errors of 25-50m which type of accuracy is low?
Geometric accuracy
What is metadata?
Information about the data set such as who created it, its precision, and the year it was created.
Interval data
Interval data places values along a regular numeric scale -elevation in Oregon. Supports addition/subtraction If it can have negative values, it is interval data Use a "color ramp" that increases color value or saturation
When classifying numeric data, which method sets the class breaks at naturally occurring gaps between groups of data?
Jenks method
Think about if you were mapping Eckerd... What data layers will you need?
Land, streets, elevation, etc.
Map Scale
Map scale is the ratio of distance on the map to the distance on the ground; it is dimensionless and can be expressed in any units (cm, in)
Can a map have shape and proportional area?
No
Can direction and distance be correct on the entire map?
No
Would the UTM projection be a good choice for making a map of the contiguous US?
No, UTMs are only accurate within the 6 degree boundaries of their zones
Nominal Data
Nominal data names or uniquely identifies objects -County names. -Airport names. -Tax ID numbers. -Parcel ID numbers. Each feature is likely to have its own value
How do you minimize MAUP
Normalizing (dividing) data by a suitable field allows data patterns to emerge ex: Farms per square mile instead of number of farms.
Ordinal Data
Ordinal data is a type of categorical data Ranks categories along an arbitrary scale Snail habitat rank: (0) Unsuitable (1) Marginal (2) Acceptable (3) ideal another example: gold, silver, bronze
Think about if you were mapping Eckerd... What vector types would you use for different data? (points, lines, polygons)
Points: trees, skate park, swings Lines: paths (trails), roads Polygon: Academic buildings, offices, dorms
Is the earth's shape closer to a sphere or spheroid?
The Earth bulges at the middle because of gravity, so it is more like a spheroid
What is the difference between a central meridian and the Prime Meridian?
The Prime Meridian (in GCS) is the line at which longitude is defined to be 0°, where a Central Meridian is the middle of a line on a map
Which coordinate system uses more than 1 types of projection?
The State Plane Coordinate System uses 3
Projections can be grouped into 3 major classes: Cylindrical, Conic, and Azimuthal. What determines these 3 classes?
The are determined by the shape of the surface onto which the GCS locations are projected.
What is the "Map extent"?
The range of x-y values displyed in the map frame
When data is stored in GIS, they have a source scale, but not a map scale because:
They have coordinates, but they do not specify how the map will be displayed
Graduated symbol maps...
Uses a symbol to show frequency or intensity of variable
Continuous
Varies over an area (rainfall, temperature, elevation)
In what ways have the sources from which GIS data are obtained changed?
We've moved from data only being on a computer's hard drive or CD to the internet
give an example of an image raster?
a geo-referenced photo of campus
Conic projection
a map created by projecting an image of Earth onto a cone placed over part of an Earth model - distortion is absent at the standard parallels and increase as you move away from the point -typically preserve area or distance and lose direction and shape
Azimuthal Projection
a map projection that is made by moving the surface features of the globe onto a plane -distortion is absent where the plane touches the globe and increases when you move away from that point -preserve area or distance and lose direction and shape
What does the "rule of thirds" mean from the field of graphic arts?
a page is cut into vertical and horizontal thirds, important elements placed on these intersections will have greater impact than if place in the center of the map
What is "negative space" in terms of a map?
blank areas on a map
Ways you can differentiate map objects
categories: shapes, line type, pattern, color or font quantity: varying symbol size, thickness or color
In the graphic user interface (GUI) of Pro, which ribbons are always visible?
core
Geographic data commonly comes in...
degrees, minutes, seconds, latitude; and degrees, minutes seconds longitude
Discrete Data
fixed to a specific point in space (county, states, cities, roads)
If you were mapping 100 rivers and wanted to show their flow volume, what would work best?
graduated thickness of the river
What type of grid shows latitude and longitude on a map?
graticule grid
Polygons
have area and perimeter, vertices at angels and corners (counties, lakes, parks, buildings)
Points
have x, y coordinates, no area, no length (springs, coves, caves)
Map Frame...
is a map placed in a layout
In ArcGIS, what is true about a geoprocessing tool?
it is software that preforms several related tasks; It is flexible, you are able to set different parameters for the tool; It is stored in something called a "toolbox"
What is a "layer" in ArcGIS Pro?
it points to the location of a spatial data set and stores info about how to display it
What is a dynamic label?
labels that are derived from a feature attribute and applied to an entire layer at once
What are some elements of a map?
legend, scale, north arrow
Graduated color....
maps (continuous data, like heat)
Unique Values...
maps are used for categorical and ordinal data
Single Symbol...
maps are used for nominal data. For shape, think about scale (how big on map) and for color and shape think about psychology.
What is a choropleth map?
maps that show elevation and bathymetry
Lines
no area, have length, can have direction; nodes on ends vertices in the middle (rivers, roads, evacuation routes, powerlines)
a layout includes...
one or more map frames, plus map elements like titles, legends, scale bars, and so on
Local datums
optimized for a country or continent or local area
world datums
optimized for the entire globe
Ratio Data
places values along a regular scale with a meaningful zero point -population of state capitals. Supports addition, subtraction, multiplication, division. Population can't have negative values, so they are ratio data
What type of data is "elevation of climate stations?
ratio
Value (HSV color model)
represents the brightness of the color (0-100)
hue (HSV color model)
represents the color on a scale of 0-360 (the color wheel)
Saturation (HSV color model)
represents the intensity of the color (0-100)
Generalization
simplifying a feature in order to store it or display it at smaller scales than its source scale; how much detail do you want to include? Price, Maribeth; Price, Maribeth. Mastering ArcGIS Pro (Page 411). McGraw-Hill Higher Education. Kindle Edition.
geometric accuracy
the accuracy with which the shape and position of features are represented; x, y accuracy; latitude + longitude Price, Maribeth; Price, Maribeth. Mastering ArcGIS Pro (Page 411). McGraw-Hill Higher Education. Kindle Edition.
logical consistency
the degree to which attribute values represent the true properties in the real world; ex: do two streets cross? Price, Maribeth; Price, Maribeth. Mastering ArcGIS Pro (Page 419). McGraw-Hill Higher Education. Kindle Edition.
thematic accuracy
the degree to which attribute values represent the true properties in the real world; ex: names, species Price, Maribeth; Price, Maribeth. Mastering ArcGIS Pro (Page 419). McGraw-Hill Higher Education. Kindle Edition.
Resolution
the degree to which attribute values represent the true properties in the real world; how detailed is the data? Price, Maribeth; Price, Maribeth. Mastering ArcGIS Pro (Page 419). McGraw-Hill Higher Education. Kindle Edition.
In Pro, what is the "reference scale"?
the scale at which the labels and symbols appear at their assigned size
If I was making a raster map of elevation, why should I consider using a stretched display method?
this will improve the display by ignoring the tails of the distribution
Think about if you were mapping Eckerd... name some attributes that you would want on the layers of the vectors?
trees: species, how many, health streets: names, width Buildings: name, area trails: length
Windows are work areas that can contain 2 types of objects: views or panes. What is the difference between these two objects?
views contain an entity to work with like a map, panes contain commands or settings
