Lesson 2 Geographic Context and Map Fundamentals
MEASURE EvaluationPHFI Training of Trainers
May 2011
Everything happens somewhere
Knowing where things happen can help us understand why things happen.
Location and Health
There is a close link between geography and health.
Question
What are some ways that people’s health can be affected by geography?
Geography can affect health through landscape, location of services, location of population in need, human interaction with landscape
Medical geography
A branch of geography that looks at the relation between location and people’s health
Concepts are useful beyond medical geography Long history of use of geography to understand
health and disease patterns.
John Snow cholera map
1854 London Used map to
illustrate cholera outbreak was centered around a pump on Broad St
Locking pump led to decrease in disease
Malaria in India
Maps
Valuable tool for displaying data and helping people understand data and direct action
Important Properties of Maps
When creating maps there are four factors that are important Scale Legend Title Source
All affect the context of data displayed and how the data is and can be INTERPRETED
Scale of a Map
What is scale?It is the ‘representative fraction’ and states the
relationship between the distance on the map and the distance on the ground
Why is scale so IMPORTANT?The scale affects the level of detail a map shows
Large-scale maps cover small areas, but can include a higher level of detail than small-scale maps which depict larger areas at lower detail. There are no precise definitions of large- or small-scale, but for most map users, the following general scale categories apply: • Large-scale: 1:250 to 1:1,000• Medium-scale: 1:1,000 to 1:10,000• Small-scale: 1:10,000 to 1:100,000• Very Small-scale: 1: 100,000 to above
Map Scale
Source: ICIMOD, 2000
Small ScaleLarge Scale
1:500,0001:50,000
Scale
What are the general rules with scale? Do not zoom below the scale as stated for the dataset (that is
scale at which the data was collected) Only integrate GIS dataset that have been collected at the same
or at a similar scale The maximum scale a dataset should be viewed is
approximately 100 times the Scale that is stated in the Metadata. For Example: Data collected at 1:5,000 should not be viewed
above 1:500,000
Title
Scale Bar
North Arrow
Legend
Data Source
TYPES OF MAP
Graduated Circle MapSize of symbol corresponds to data.Advantages:• Easily see extreme ends of the
data distribution• Geographic patterns emerge
Disadvantages• Can be challenging to
differentiate the middle of the distribution since the eye can’t easily detect small differences in size
ChoroplethPolygons are shaded to match data distributionAdvantages:• Easy to see geographic
distribution• Easy for most people to
interpret
Disadvantages• Polygons can hide uneven
distributions within boundaries• If patterns/colors aren’t chosen
wisely the map can be difficult to interpret
Continuous surface mapsData is distributed continuously across spaceAdvantages:• Very easy to see hot spots or
areas that deviate from other areas
Disadvantages• Not all data can be distributed
continuously
Other typesWith advanced software it’s possible to produce diagram maps that display data using charts.
Advantages• Effectively displays complex
information• Lots of information on each
map
Disadvantages• Can have too much information• Can be difficult to structure data
to produce such maps• Requires an advanced GIS
Which map style should you use?
Depends on type of data you have What purpose you want the map to serve Sometimes a matter of experimentation to find
the map style that best fits the data and purpose of the map
It’s important to pick the type of map that makes the data most useful
Basic cartographic concepts
Map Design Cartographic standards Generalization Graphic Variables Use of Color Classification of Data Methods of Mapping
Map making is both science and art.
Maps influence people’s perception of space. This influence is partly because of convention and partly because of the graphics used.
People understand the world differently, express this understanding differently in maps, and gain different understanding from the maps.
Map Design
Cartographic standardsThere are cartographic standards that have emerged that make it easier to interpret and read maps.
These standards do not have to be followed, but if they aren’t your map may be less readable.
Administrative BoundariesMost often black or gray.
The higher the administrative unit the thicker the line
RoadsColor and line styles to represent road type with major roads being thicker or more distinctively colored than minor roads.
Rivers and LakesBlueStreams dashed lines light blue
Map Design
Generalization Maps contain a
certain level of detail depending upon its scale and purpose.
Sometimes the map maker will need to simplify features to make them more readable.
Use of Color Color perception has psychological, physiological and conventional aspects.
It has been noted that it is difficult to perceive color in small areas, and more contrast is perceived between some colors than between others.
In addition to distinguishing nominal categories, color differences are also used to show deviations or gradation.
Hue
Saturation
Intensity
Source: ICIMOD 2000
Use of Color
Color blindness 5-8% of men 0.5% of women
Classification of Data The representation of data for mapping will depend on the measurement scale of the data.
Nominal scale: The differences in data are only of qualitative nature, e.g., differences in facility type, land use or geology.
Interval scale: Both the hierarchy and the exact distance is known, but it will not be possible to know the ratios, e.g., the temperature or the altitude values. Ratio scale: Data can be measured on a ratio measurement scale, e.g., the number of children in a family or income.
Ordinal scale: Only the order of the attribute values is known, such as more than or less than, “small - medium – large” or “cool - tepid - hot”.
Source: ICIMOD 2000
Making an effective map is a matter of finding the right balance between the limitations of the data, the needs of the map reader and the message you, as the map maker, want to convey.
Issues to Remember Maps can LIE!! Maps are just one person’s representation of the
“real world” Like any source of information they can be
misleading especially when used out of context How maps can be deceiving
Inappropriate Legend Inappropriate Scale
Source: ICIMOD, 2000
Key points
Everything happens somewhere Geography is a common denominator across
human activity There are different types of maps, picking the
right style is balancing the needs of the reader, the data and the message you as mapmaker want to convey.
Key points
The mapmaker can use colors, symbology among other techniques to make maps readable to the audience.
Any questions?