Maps and Diagrams | SNHS Geography

Maps & Diagrams

It often makes sense, in Geography, to present information on a map. This can range from a simple map in an atlas up to extensive geographical information systems, which allow data to be stored, analysed and presented on much more complex digital maps.

We will cover a range of different styles of maps and diagrams:

Sketch Maps
Isoline Maps

Dot Maps
Choropleth Maps

Proportional Symbols Maps
Flow Line Maps

Sphere of Influence Maps
Transects & Cross Sections

Annotations

Annotation means to add notes to photographs, overlays, field sketches, graphs, maps, diagrams or data tables. The purpose is to highlight relevant information to the reader.

For example, a sketch map created using an overlay could include annotations which focus the reader on relevant features, such as roads, in a transport study.

The annotations can be added by hand or digitally.

Sometimes an annotated photograph isn’t as valuable as a field sketch. In the same way, an annotated map may be superseded by a sketch map. These further draw the reader’s attention to the relevant information and remove all the “noise” from the background.

Useful when:

There are clear features to be identified – not too many and not too few.
The annotations, sketch maps or field sketches contribute to the reader’s understanding of the written information. That means they’re not necessary for very simple things (e.g. I saw a cliff) and that they may not be very appropriate for very complicated things.
Linked to written text.
They are carefully planned – what information will you include and highlight – and what information are you removing as it’s not relevant?
The position of the annotations don’t make things too busy or overlapping.

Annotations can be added using a tracing overlay (such as in your AH exam) or digitally, using software such as Google Slides.

Question: What are the main features required in a field sketch?

Watch this video from GeoBus and include a list in your notes.

Worked example

Starting at the top of the diagram and working down the page, we can see that the input into the drainage basin is precipitation. Most of the precipitation falls onto the vegetation and from there some of it is lost through evapotranspiration. Of the remainder, the water flows from the vegetation down into surface depressions where again some is lost through evapotranspiration and some becomes overland flow into channel storage.

The rest infiltrates into the soil to become soil moisture and again some is lost through evapotranspiration and some becomes throughflow into channel storage. Some of the soil moisture then percolates deep into the rocks to become groundwater which flows into channel storage.

Imagine having to read the above paragraph without the data being presented graphically. It would be mind boggling! This demonstrates a good use of a systems diagram.

By using the same terms as the diagram, and putting them in bold, it’s easy to refer between the diagram and text.

Activity

This text talks about the inputs, stores, outputs and transfers involved in the glacial system. Using the terms in the text, create a systems diagram.

The glacial system consists of inputs, stores, transfers and outputs. Understanding the connections and relationships between the different components of the system helps indicate how a change in one component results in consequential changes throughout the system.

Inputs – The main input to the glacier system is through precipitation in the form of snow. Ice and snow can also be inputted to the glacial system through avalanches which can occur both naturally and due to human activity in mountain areas. Inputs to a glacier result in accumulation.

Stores – The mass of ice within a glacier is a store that can be added to (accumulation) or lost (ablation). Material that is carried by the glacier is also known as a store.

Transfer – The transfer is the movement of a glacier due to gravity, gradient and increasing accumulation at the glacier source. In mountainous areas this movement is much quicker than that of ice sheets, which are often on a flatter surface. The main movement is downhill although, unlike water, ice has the capacity to move uphill if the ice pressure behind is great enough, resulting in the over-deepening of glaciated valleys.

Outputs – The main output is the loss of water vapour from the evaporation of water from the glacier’s surface. If, under certain circumstances, snow and ice converts directly to water vapour without going through the liquid water stage it is known as sublimation.

Another output is calving which is where blocks of ice break off at a glacier’s snout. Usually this occurs where glaciers end in lakes or the sea, but it can also occur when ice falls off the end of a hanging valley glacier.

The other main water output from a glacier is where water leaves the snout of the glacier in liquid form as meltwater streams.

All these outputs from a glacier’s ice store are known as ablation. Solid material leaving the glacier can also be included as an output. As a glacier retreats (melts towards its source), rocky material will be washed out of the glacier, known as moraine.

Choropleth Maps

Choropleth maps show data across different unit areas.

The unit area will depend on the scale of the map – it could be a whole country or a smaller region.

Useful when:

Data is assigned to different regions/areas.
You are identifying patterns across a town, region or country (e.g. most of the areas in the south have lower poverty).
The data is ordinal, interval or ratio.
Colours chosen are appropriate; often this means graduated shades of one colour, but in some cases (e.g. temperature or things that are both positive and negative) these can be a range of e.g. red to blue. Pick colours appropriately – don’t use red when talking about ice coverage and brown when looking at areas that have been reforested.

Question: Which of these sets of data would best be presented as on a choropleth map?

A – Changes in life expectancy (increase or decrease) across the US state of Alaska since 2020.

B – The reasons that people have chosen to live in a new housing development.

C – The angle of slopes across a raised beach.

Worked example

The decision about how to group or categorise your data is often the hardest. In this population density map of Nepal, there are enough groups that it is useful data, but not too many that it becomes complicated.

The map makers have made the decision to have uneven groupings, i.e.:

Most of the groups have a range of 100
One of the groups has a range of 700
They have chosen to include a “above…” and “less than…” category

Ideally, choropleth maps should have categories with equal ranges, but sometimes map makers make deliberate decisions, based on the data they’re working with, to do otherwise. Common groupings include:

All groups having the same range
All groups increasing in range evenly
Standard deviations
Natural breaks
Equal number of values/regions in each group

The darkest colour is usually used for the highest; in this case the capital city of Kathmandu stands out as having a very high population density.

Choropleth maps display data for regions/areas, giving each value or group of values a different colour.

The maps are visually effective as you can see a large amount of information and general patterns.
They can be used to easily compare regions e.g. countries. However, it only gives an idea of which group the data is in, not the exact value – a proportional symbols map would show the exact number.
The map doesn’t show any variation within the area – it uses an average and assumes that the whole region has the same value.
The boundaries chosen (e.g. countries) might give artificial divisions, whereas in reality the change will be more gradual.
Depending on the colours chosen it can be difficult to distinguish between the shading used on the map.
Decisions about how to make the divisions can be tricky; and could be systematic (same data range for each division) or stratified (data in natural groups/divisions).

Activity

Nitrous Dioxide (NO₂) is a gas, formed during combustion, which is the major contributor to air pollution in cities. It is a respiratory irritant, which worsens asthma and can contribute to infections in the lungs. It also contributes to smog and acid rain.

Some cities around the world have implemented low emissions zones (LEZ) to reduce the impact of air pollution. One of the cities which has done this is Glasgow.

As part of the work done to plan the LEZ, areas across Glasgow had their NO₂ levels measured.

Collect a print out of the map of Glasgow and create a choropleth map of the data. You will have to decide on the groupings/key and pick an appropriate colour scheme.

Proportional Symbols Maps

These display data using symbols or pictures which are different sizes. For example, a circle may appear bigger if the data value is larger.

There are two kinds:

Absolute scaling – where the symbols are mathematically proportional. e.g. a circle representing 2 million people is twice the area of a circle representing 1 million people.
Range grading – where each size of circle is assigned to a value/range of values, like in a choropleth map.

Useful when:

Data is point data – it can be tied to a specific place.
The symbols are far enough apart that they are all readable. This could be done by choosing an appropriate scale or not including small values.
Geometric shapes (circle, square, star) can be used, but thematic pictorial symbols can also be used to match the theme of the map. For example, a map of airport departures might use scaled plane pictures and a map of population might use stick figures.
Transparent symbols (as in the proportional-squares map) can be used, but too much overlap can cause difficulties with interpreting data.

Look through an atlas and find 5 examples of proportional symbols maps. What kind of data is displayed in this way?

Worked example

This is an example of an aggregated scale map, where the symbols are truly proportional. Only countries with urban populations more than 1 million are included, which removes the problem of overlapping symbols. Additionally, colour has been used to denote different continents.

The key is useful and includes some examples of circle size so that rough estimates can be easily made. There are some places (e.g. south-eastern Europe and central America) where the scale of the map makes it difficult to see the populations.

As the data is averaged across the whole country, the central point of each country has been used.

Proportional Symbols maps use different sized shapes to represent data.

They can summarise a large data set in a visual form.
The symbols are easy to interpret because each symbol is proportional to its value.
Deciding on a suitable scale for the symbols may not be easy if there is a large range of values. If the scale is too large then some symbols may overlap and be difficult to read.
Transparent symbols could be used to lessen issues of overlapping.
The size of the symbol may lead to less accurate positioning of the symbol on the map.
They can be used for a precise location or a geographic area (e.g. country, state, region). If used for a geographic area they tend to be placed in the centre.
Proportional symbols maps can become cluttered.

Activity

The emissions of NO₂ were measured again a year after the introduction of the LEZ. This was done using diffusion tubes, a low-cost way to sample pollutants over a 4 week period. The tubes are then analysed at a lab to determine the levels of NO₂

The LEZ was enforced from 1 June 2023.

The results from after the introduction of the LEZ are shown in the table below. Draw a proportional symbols map of the results and answer the questions.

You will need to decide whether to use absolute scaling or range grading.

1) Glasgow’s LEZ lies entirely within the Anderston/City ward of the map. By what percentage have the emissions here decreased?

2) Many of the other wards have also seen their NO2 levels decrease. Suggest two reasons that this might be.

3) Calton (Ward 9) has not seen a decrease in NO2 levels. Referring to the map, suggest why this might be.

4) The Glasgow LEZ was introduced with the aim of reducing air pollution in the city centre. What other social, economic or environmental benefits come from the introduction of LEZs?

4) Compare the choropleth and proportional symbols maps you have produced. Which technique works best to display this data? Give two reasons why.

Isoline maps

These maps use lines that joint points of equal value. Often, where only one kind of information is included, colour is added to help the visualisation of the data. In other circumstanceswhere lots of information is included in the map (e.g. OS maps or synoptic charts), isolines will remain as lines with their values stated.

Useful when:

A large amount of data is known for locations across a spatial area.
There are gradual changes and patterns over the area.
Data would otherwise cross boundary lines (e.g. country borders).
Care is taken to join up points carefully – this is technically a subjective process and is likely to be done differently by each person.

Some names to be familiar with:

Isobars – lines of equal pressure (found on synoptic charts)
Isohyets – lines of equal rainfall
Isotherms – lines of equal temperature
Isovels – lines of equal velocity (e.g. river velocity)
Contour lines – lines of equal altitude

Look through an atlas and around the Geography classroom to find 5 examples of isoline maps. What kind of data is displayed in this way?

Worked example

This video takes you through how to complete an example of an isovel map.

Isoline maps use lines that join points of equal value.

Examples include contours on a map, isobars on a synoptic chart and
isotherms on a climate map.
They can be used when the data changes gradually in space.
They cross boundary lines (e.g. country borders) so work across large
regions.
Isoline maps are useful when showing gradual changes and patterns over large areas.
They use fix intervals so changes can be easily identified (e.g. if the height changes over a small area there will be many isolines close together).
Colour/shading can be added to enhance patterns and trends and they can be used with most base maps.
The “joining up” of lines between points can be subjective and it’s likely to be done differently by each person.
They also require a very large amount of data and assume that every point between the lines is equal, particularly when shaded or coloured to reinforce that.
The greater the division between lines the more detailed the data, but the harder it is to interpret the data.

Activity

Collect a sheet from your teacher. It shows spot heights which have been taken across an area.

Create an isoline map showing the topography of the area. You could then add colour (choose shades of colour which make sense for high/low land).

Dot maps

Dot maps show spatial distribution, with each dot representing a specific population (e.g. one incident, 100 people, 10 deer).

Useful when:

You want to identify areas with clusters or gaps in the data.
You have a lot of data to plot.
The data is spread over an area which makes sense – for example, it’s not a very helpful method if your data is collected in a simple square as it’s hard to make links between where the cluster is and where that is in the real world.

Question: Which of these sets of data would best be presented as a dot map?

A – The location of profitable dairy farms across Dumfries and Galloway.

B – The breakdown of ages of people across an electoral area.

C – Incidences of schistosomiaosis across Rwanda.

Worked Example & Activity

On this dot density map of the population of the United States, one dot is equal to 7500 people.

Using the map (below), answer these questions.

Using an atlas (or a map of the United States), give the location of three clusters of data – i.e. where lots of people live.

There is a large cluster of data in the south of California, in the areas around Los Angeles and San Diego.
Now do two of your own…

Describe three places where there are gaps in the data – i.e. where few people live.

There is a gap in the data in southern Nevada, where some regions have only 7500 people.
Now do two of your own…

Referring to other maps in your atlas, suggest three reasons which might be influencing the population distribution across the United States.
You will often be asked, in AH exams, to identify patterns which exist between different types of maps.

Referring to this choropleth map of educational attainment in the US:

a) suggest whether you would consider there to be a relationship between population density and educational attainment.

b) suggest whether this is a positive or negative relationship.

c) give at least one reason that may explain why this relationship exists.

Flow Line Maps

These show data which has a direction. The arrows/lines used are proportional; the bigger they are, the more data which is moving in that direction.

Useful when:

Data is directional – often flowing “out” from one point or “in” to one point.
The proportional width of the lines is important – showing where most data is coming from or going to.
The point of the arrow shows the destination.
Care is taken to choose a scale and number of arrows so that there is not major overlapping.
Base maps are kept very simple.

Question: Which two these data sets would be best shown as a flow line map?

A – The major routes of drug trafficking across the world

B – The destinations and movements of tourists across the world

C – The mode of travel of spectators who travelled to watch a football match in Aberdeen.

Worked Example

One of the most common uses of flow line maps is in presenting data on the subject of migration.

In your Higher course, you studied the voluntary migration of people from India to Qatar. The data shown here shows the donor countries of people who live in Qatar.

This data can be used to create a flow line map. For this, I have focussed on the top 6 donor countries as adding more would be utter chaos!

Step 1: Locate a suitable base map

This should have only basic information on it – the less the better.

Step 2: Plot on the start and end locations

Usually we use the rough centre of a country.

Step 3: If using proportional symbols, decide on a suitable scale

This is probably the hardest step, so feel free to sketch it out or try different things. In a similar way to proportional symbols maps, these can be absolute scaled or range graded. If you’re making your map electronically, use the line width or shape size to scale the arrows easily. In this example, I used that 1px line width = 100,000 people.

Step 4: Plot the lines

Being careful to avoid overlap where you can, plot the lines from the start locations to the end locations

Step 5: Key

Remember to add a key and title to your map.

Activity

As part of the Scottish Census, data was collected about the movement of commuters between their home and place of work.

The Highlands and Islands Transport Partnership (HITRANS) have used this data as part of planning the Inverness Active Travel Masterplan. They wish to use a flow line map to present data from Inverness.

You can choose to do this electronically (here’s the map) or on paper.

The data in the table shows the number of commuters who use bicycles to get to central Inverness (the dot outlined in black).

Create a flow-line map using the data. You will have to consider the proportional width and locations of the flow lines/arrows, to avoid overlap.