Human Intervention and GIS

How people change a glaciated landscape

The Lake District’s valleys and lakes were shaped by glaciers, but people continue to change this landscape. Human intervention includes constructing reservoirs, extracting rock and developing facilities for visitors. Investigating its impact means examining what has changed, where the change occurs and what consequences it has for the landscape.

Reservoir construction provides a clear example. Thirlmere and Haweswater are used for water supply. Creating Haweswater involved flooding the Mardale Valley, changing the valley’s land cover and affecting its ecosystem. Tourism produces different pressures: paths, buildings and other facilities support visitors, while visitor activity can contribute to soil erosion, pollution and erosion of lake banks. Quarrying for materials such as slate and limestone also changes the landscape by removing rock.

Maps help locate these interventions. GIS allows geographical information to be combined and compared, making it easier to investigate their extent and their relationship with the surrounding landscape.

Using OS maps at two scales

An Ordnance Survey map can show human features alongside the terrain. Read its key to identify the symbols used for roads, paths, buildings and other features rather than guessing from their appearance. Maps represent features using points, such as a symbol marking a facility; lines, such as roads and paths; and areas, such as woodland or water. OS tourist features are shown in light blue, but the key is needed to identify the particular feature.

At 1:25,000, 1 cm on the map represents 25,000 cm on the ground, or 250 m. At 1:50,000, 1 cm represents 500 m. A 1:25,000 map therefore shows an area at a larger scale and generally provides more local detail; a 1:50,000 map is useful for examining a wider area.

For a constructed illustration, imagine a new access road drawn as a straight 4 cm line. It represents $4 \times 250 = 1000$ m, or 1 km, on a 1:25,000 map, but $4 \times 500 = 2000$ m, or 2 km, on a 1:50,000 map. On an actual map, measure the bends of a winding road rather than using only the straight-line distance between its ends. On a digital map that has been resized, use its scale bar or distance-measuring tool rather than assuming that a screen centimetre retains the original printed scale.

To investigate a reservoir, locate the water body, surrounding slopes, nearby roads and settlements. This establishes the setting of the intervention. To investigate tourism, examine how paths and access roads connect visitor facilities with lakes and upland slopes. Their distribution can suggest where visitor pressure might be concentrated, but the map alone does not measure erosion or pollution.

Comparing maps to identify change

A useful investigation begins with a focused question, such as: How has reservoir construction changed land cover in a glaciated valley?

Compare maps from before and after the intervention, using the same area and accounting for differences in scale. Locate features common to both maps so that you compare the same places. Look for changes such as water replacing land, altered roads or the disappearance of buildings from the mapped area.

A feature missing from a later map has not necessarily disappeared on the ground. Maps simplify information to remain readable: a small building shown at a larger scale might be omitted at a smaller scale. Check whether an apparent change could result from differences in map detail rather than human intervention.

Separate the observation from its explanation. An increase in the area mapped as water is evidence of changed land cover. Flooding previously dry land would also alter habitats, but a map of water extent alone cannot establish which species were affected or how much biodiversity changed. That requires ecological evidence.

For Haweswater, the flooding of Mardale Valley provides the real example of this relationship: water supply infrastructure changed both the landscape and its ecosystem.

Using GIS layers to investigate impacts

GIS stores, displays and analyses information linked to locations. Different kinds of information can be displayed as layers, allowing you to examine their relationships. For a reservoir investigation, useful layers could include water extent at two dates, roads, settlements and land cover. Overlaying them means displaying them together in the same geographical position.

First, check that the layers cover the same area and line up correctly. Give the two water layers distinct colours and use their key to distinguish them. Switch one layer on and off, adjust its transparency or use a swipe tool to reveal the layer beneath. Look for places covered by water at the later date but not at the earlier one. Adding the earlier land-cover layer helps identify what occupied those places before flooding.

GIS can also measure the change. Water may be represented by an area boundary or by cells classified as water in a satellite image. Identify the water area for each date and use the GIS area calculation, keeping the units the same. When using classified imagery, compare the classification with the original image: clouds or incorrectly classified cells can distort the result.

Consider a clearly fictional upland valley. Suppose its mapped water area is 0.5 km² before an intervention and 1.5 km² afterwards. Subtracting the earlier area from the later area gives $1.5 - 0.5 = 1.0$ km²: a net increase in water area. The overlay shows where the change occurred, while the calculation shows its size.

The same approach can investigate tourism. Overlaying paths and visitor facilities with surveyed erosion locations could reveal whether erosion is concentrated along heavily used routes. An overlap is evidence of a spatial relationship, but does not by itself prove that tourism caused all the erosion: slope, rainfall and surface material may also matter.

Reaching a supported conclusion

A strong conclusion connects intervention, mapped change and impact. Reservoir construction can replace valley land with water and alter habitats; visitor access can concentrate pressure along particular routes; quarrying can remove rock and change the appearance of slopes.

Transfer the methods to authentic OS maps and GIS information by checking the key, scale, dates and data coverage. For water comparisons, check the season and weather conditions too: a different water extent could reflect rainfall or drought rather than construction. Changes that began before an intervention cannot be attributed entirely to that intervention.

Use photographs, field observations or environmental measurements where the impact itself—such as pollution or footpath erosion—is not established by the mapped evidence. Maps and GIS reveal patterns and measurable changes; additional evidence helps explain their causes and consequences.