Flashcards in Map Styles Deck (17):
What are reference maps?
Emphasis on spatial and attribute accuracy.
Nautical Charts, Topographic Maps, Aeronautical Charts
What are thematic maps?
Highlights patterns and distributions for spatial analysis
Choropleth, Dots, Graduated Symbol
What are symbols for nominal and qualitative distinctions?
What are symbols for ordered quantitative distinctions?
What are choropleth maps?
Very simple value (choros) by Area (plethos) Maps indicate the amount of something in a predefined place like a county, census tract, block group or country. The design of these maps is based on two factors:
1) Classification (creating categories)
2) Symbolization (creating symbols)
Research has shown that the maximum number of grey shades that can be distinguished accurately is about ___. Choropleth maps rely on the user to be able to ________-.
state positively which group each area falls into
For categories, Color use can extend the number of categories a little but, these are ranked data, so widely divergent colors are ________.
Not a good strategy as they do not meet the expectations of the reader
For choropleth maps, what are the three categorization cut points?
When do you use equal interval?
If you want equal parts of the data range in each category
Each category is the same width, not good if outliers in the data (extremely low or high values)
When do you use equal number?
If you want equal representation of categories among map areas
An equal number of areas are in each category, does not consider the values only the order – ordinal
When do you use natural breaks?
If you want to be sure that the categories are most internally similar
Determine largest gaps in the data, also can be a problem if outliers exist
What is the formula for equal intervals?
(max - min)/ number = width
What is the formula for equal number?
sort values low to high. Divide the number of values by the number of categories
number of values/ number of categories = number
How do you compute natural breaks?
Sort Data low to high
Compute the “breaks”
Place category breaks at the “n-1” largest breaks:
When making do maps, what are the two decisions you need to make?
Classification: The number of items per dot – we are mapping counts of objects such as people, so we have too many to show each individual. The classification concept is very simple:
Take the count of people/cows/etc. and divide by the dot value to get the number of dots.Look over the number of dots to see if they are: Enough in small counts. Few enough in large counts. The outcome is not always so simple.
Symbolization: the dot size is variable for visibility, but dots usually exaggerate actual size of the objects they map.
Instead of placing a dot for every item, what can you do?
Make a symbol larger in the proportion to the number
Base size: what is the smallest symbol size to be?
Base Value – how many items will that size represent