Geography - Scale and Generalization
Scale Relationships
*RF* *Word Statement* 1:1200 100 feet to an inch 1:24,000 2,000feet to an inch 1:50,000 ½ kmper centimeter 1:63,360 1 mile to an inch 1:100,000 1 km percentimeter 1:250,000 4 miles to an inch(aprx) 1:500,000 5 km per centimeter 1:1,000,000 10 km per centimeter
Examples of Representative Fraction
-1:24,000 -1: 62,500 -1:100,000 -1: 200,000
Graphical Scale
-A line drawn on a map subdivided into units
What generalizations are made on maps based on their purpose?
-Change in content, despite similar scale -Content adjusted to make it useful and still be able to recognize features
Why should determining distance, direction, and measurements only be done with large scale maps?
-Change in scale across surface is negligible -Close geometric representation of the earth
Verbal Scale
-Gives a quick idea of size relationship +Involves Units +Direct Comparison
What are digital examples of multiscale maps?
-Google Maps -Map Quest
Reference Material
-Graticule Lines -Section Lines -Road Lines Ex) On an atlas, the map distance between parallels 40°and 41°North is 24.5 millimeters, what is the scale of the map? *Answer in slideshow
What are the methods to determining the ground distance between two points?
-Known terrestrial features -Reference material -Map comparison
Map Comparison
-Map of known scale must cover at least a portion of the area
Using Reference Fraction to find distance
-Measure the distance on the map with a ruler. -Use the scale to find out the distance in real life: -convert X cm to meters and then to kilometers
Combination (Generalization Technique)
-Merging two or more similar features into a single symbol
Examples of Verbal Scale
-RF of 1:24,000 can be expressed as " 1 inch to 2000 feet" +1 inch on the map is 24,000 inches on the ground (or 2,000 feet) -RF of 1:100,000 can be expressed as "1 centimeter to 1 kilometer" +1 centimeter on the map is 100,000 centimeters on the ground (or 1KM)
Representative Fraction
-Ratio between map and ground distance +Dimensionless (unit free) +Used with any linear measurement unit such as feet, meters, or miles
What are components of expressing scale?
-Representative Fraction (RF) -Verbal Scale -Graphical Scale (Scale Bar)
Selection (Generalization Technique)
-Retention of the more important features -Elimination of less important features
Generalization Techniques
-Selection -Simplification -Combination -Shift and Exaggeration
Multiscale Maps
-Series of maps at smaller of larger scales -Different maps cached and pre-rendered as collection of tiles ready for display
Simplification (Generalization Technique)
-Simplification of the shape features being retained -Enough details left so that major characteristics are identifiable
If interested in a general presentation of a large area (state, country, globe, etc), choose a _________ scale map. Why?
-Small -Scale changes continuously across small scale maps +Given scale only accurate at particular points or lines
The ___________ the scale of the map, the greater amount of generalization required. Why?
-Smaller -Amount of space available to show features decreases as scale decreases
Using the RF (1/x) as 1, it follows that the _______ the denominator, the __________ to a 1 to 1 ratio.
-Smaller -Closer Ex) + 1:200,000 (larger scale) + 1:400,000 (smaller scale)
Known terrestrial features
-Some features have standard lengths +U.S. football field (100 yards)
Shift and Exaggeration (Generalization Technique)
-The need to slightly move and aggrandize features in order to distinguish them and increase legibility
What is generalization of maps influenced by?
-The purpose of the map
Methods of Converting Scales
-Verbal Scale to Representative Fraction -From Representative Fraction to Verbal Scale *See slideshow for examples
How is representative fraction displayed?
1/x or 1:x
What does a graphical scale resemble?
A small ruler printed on a map
What does graphical scale allow?
Allows to determine distance in whole and fraction units
Example of Map Comparison: On a map with RF 1:125,000, two features are 50 mm apart. On a map with unknown scale, the same features are 100 mm apart. What is the scale of the unknown map?
Answer in slide show
How can determining map scale be done?
By knowing the ground distance between two points
Many wooded areas being merged into one on a map is an example of the generalization technique of _________________.
Combination
In representative fraction, what does the denominator represent?
Denominator represents distance on ground
"Large" or "small" comes from the value of the __________.
Fraction
Every map, to some extent, has been ______________.
Generalized
What is a danger of the generalization technique of combination?
Hiding separation
How does graphical scale change?
In direct proportion to the physical size of the map
Scale has an __________ relationship with areal extent.
Inverse
The generalization technique of shifting and exaggeration is usually done on ____________ scale maps.
Large
When determining distance, direction, and measurements in general, you should only do so with __________ scale maps.
Large
On multiscale maps, zooming out results in ___________ details.
Less
On multiscale maps, zooming in results in ___________ details.
More
On a graphical scale, do marks represent a particular unit?
No
In representative fraction, what does the numerator represent?
Numerator represents maps distance
When using longitudinal lines, convergence towards the ______ must be taken into consideration.
Pole
On multiscale maps, what is information shown dependent on?
Scale or level of zoom
In a series of lakes, smaller lakes being removed on a map is an example of the generalization technique of ______________.
Selection
Road features in a narrow valley on a map is an example of the generalization technique of ________________.
Shift and Exaggerate
Shorelines of a lake made less complex at smaller scales on a map is an example of the generalization technique of ______________.
Simplification
What must one be aware of with the generalization technique of selection?
That some smaller features are not shown
What is a Cartographic Scale?
The ratio of the size of objects on a map compared to their size in the real world (Amount of size reduction)
What is generalization?
The simplification of features on a map
How is verbal scale displayed?
X inches to a mile
