GIS Exam Questions PDF

1\. In GIS, geographic problems are assessed. a\. What is meant with a geographic problem -- please define? b\. With so many problems being geographic, there is a need to categorise them. Mention at least three methods for categorising geographic problems. c\. For each of the above methods, list...

1\. In GIS, geographic problems are assessed. a\. What is meant with a geographic problem -- please define? b\. With so many problems being geographic, there is a need to categorise them. Mention at least three methods for categorising geographic problems. c\. For each of the above methods, list the associated categories and provide examples within each category. a: Problems that involve an aspect of location, either in the information used to solve them, or in the solutions themselves, are termed geographic problems. b: Scale, or geographic detail. Intent, or purpose. Time-scale, or priority. c1: Scale, or geographic detail: Micro level -- the coordinate system of crystalline structure. Local -- cities, forests, parks. Regional -- Baltic runoff, nationwide flu epidemic. Global -- global warming, bird flu pandemic. c2: Intent, or purpose: Practical, urgent -- money, emergency. Curiosity driven -- continental drift, glacial withdrawal, historic migration patterns (little urgency). c3: Time-scale: Operational -- the smooth functioning of an organization. Tactical -- where to cut trees in next year's forest harvesting plan. Strategic -- organizational long-term direction. 2\. At its most primitive, what does an atom of geographic data (a datum) contain? How does an attribute value relate to a geographic datum? Geographic attributes are classified in accordance with their scale type -- which scale type is special for geographic data, and why is it special? At its most primitive, an atom of geographic data links a position (in space and time) with some descriptive property called its attribute. Geographic attributes have a value given at a scale, where the type of scale normally ranges from nominal to ratio. In the geographic system of 1 coordinates, however, circular degrees are introduced, which calls for a cyclic attribute scale. The cyclic scale is mathematically peculiar, since it "bites itself in the tail". 3\. The fundamental problem that is being solved with a GIS, is to simplify reality in order to fit it into a computer, hence reducing an infinite amount of data (plural of datum) into a finite set. This simplification is basically made by two separate methods that generate different types of data. a\. What are the methods? b\. Exactly how do they simplify geographic reality? c\. What are the two corresponding methods of representing geographic data in a computer called. d\. In the two respective methods of digital representation, exactly how is the amount of information for representing geographic objects regulated? a: Spatial averaging by pixel (tessellation) and using the fact that many attributes remain constant over large areas. b: In spatial averaging by pixel, attribute values within a square pixel are set constant. Most often they are replaced with the average attribute value. In the constant value perception, geography is being represented with discrete objects. c: Raster and vector representation respectively. d: In raster representation, pixel size determines information density. In vector representation, the number of points used to represent a geographic object determines information density. 4\. A lot of geographic objects are fuzzy, meaning that it is difficult to know exactly where they start and end. In addition, their extent may change annually or continuously, e.g. when a delta changes due to sedimentation. In the case of wetland lakes, they are often surrounded by wetlands and should, perhaps, be considered more as a moisture gradient ranging from dry land to the permanently wet, than as a well defined geographic entity. How would you choose to represent a well defined lake entity that never changes its extent, and how would you change this method of representation into the fuzzy method required in the case of wetland lakes? Please provide an example with categorisation and the associated attribute table. The extent of a lake that never changes may be perfectly represented with a vector polygon. In the fuzzy situation, a raster would do better, where the lake is defined in accordance with a wetness index, perhaps categorized into: 1: Always dry, 2: Annually flooded, 3: Submerse vegetation, 4: Water permanently present at a maximum depth of one meter, 5: Water permanently present at a depth exceeding one meter. 5\. What is a secant cylindrical transversal projection? Why is such a projection particularly suitable in a south-to-north oriented nation like Sweden? Exactly what is gained with a secant projection? How does the term "central meridian" relate to the above? In a secant cylindrical transverse projection, geographic coordinates are projected onto a plane wrapped around the Earth in the form of a cylinder that touches the Earth along a meridian (orthogonal to the Equator). In a tangential projection, the diameter of the cylinder coincides with the diameter of the planet, whereas a secant cylinder is smaller than the diameter of the Earth, thus cutting through its surface along two meridians. Since projection scale is 1:1 at the tangent meridian, smaller than 1:1 in-between secant tangents, and larger than 1:1 outside tangents, the average projection error is smaller in the case of a secant projection, as compared with the 2 tangential ditto. When adapted to a specific region, the transversal cylinder is rotated to fit the region's central meridian. Hence, the tangent meridian of a tangential projection coincides with the central meridian, whereas the central meridian is located in-between secant meridians. With the curvature of Sweden being predominantly situated in the south-north direction, it is predominantly covered with a transversal cylindrical projection, and therefore holds a relatively small average projection error. 6\. Formal reference maps constitute the basis for most nation's official territorial representation. Although the scale varies from one nation to another, 1:50,000 is typical. Although they have different names, like The terrain map. The topography map, The general map, etc., they are alike with respect to their content. What classes of geographic information does a typical 1:50,000 terrain map contain? In non-arid regions, what is it's referential skeleton? What is the referential skeleton used for? What is the map typically used for? A terrain map is typically constituted by landscape hydrology, land-cover, infrastructure, urban structures, topography, etc. Where water is abundant, hydrology typically constitutes the map skeleton. In arid areas, this may be replaced with infrastructure. The referential skeleton is used for orientation -- hydrologic landscape elements are the main geographic reference in a post glacial nation like Sweden. The terrain map is typically used for physical planning, geographic analysis, geographic presentation, and for geographic orientation. 7\. In geographic positioning, single-station real-time kinematics (RTK) is gradually being replaced with network RTK. Explain the methodological difference (e.g. by making a drawing), and also explain how network RTK stations collaborate in order to minimise positional error. How does SWEPOS relate to the two mentioned methods of differential GPS? Single-station RTK uses the GPS satellites in combination with a GPS transmitter installed at a known reference position, whereas network RTK operates with GPS satellites in combination with multiple reference stations. With a collation of reference stations covering a region, they provide spatially varying compensation regarding atmospheric sources of positional error, such as ionic activity and electric conductivity. SWEPOS is the national Swedish network of positional reference stations. 8\. Mention at least two different passive sensors for remote sensing, and also at least two active sensors. For each of the mentioned sensor system, provide an example on what is being sensed. Passive sensors utilize the reflectance of external energy sources (like the sun) or blackbody radiation, whereas active sensors utilise the reflectance of a signal emitted by the sensor-system itself. Passive infrared satellite-mounted sensors like LANDSAT, that are used for depicting vegetation. Conventional passive digital cameras mounted in airplanes for producing highly resolved reference information (on changing landscapes). Active airplane-mounted RADAR sensors for depicting elevation. Active ship-mounted SONAR sensors for depicting sea-floor elevation. 9\. What is a choropleth map? What is meant with multivariate representation? What is a cartogram? In each case, please provide an example. A choropleth map holds a polygon representation where each polygon holds a constant attribute value. For example, in the respective cases of nominal and ratio scales, a county map of Sweden, or a county-wise representation of inhabitant numbers, are typical choropleths. 3 In multivariate representation, individual symbols carry multiple attribute values. An example might be a naval chart where current is represented with a field of arrows that are coded for speed with their respective colours, and for direction with their respective orientations. Cartograms are maps that lack planimetric correctness, and distort area or distance in the interest of some specific objective. An everyday example is underground or bus-line cartograms, where dwindling lines have been straightened out for the sake of clarity. 10\. Measuring length on a plane projection of ellipsoid Earth is due to several sources of error. Mention at least three fundamentally different sources, and explain the nature of the associated error. Choice of distance metric: With the Pythagorean metric being applicable when the shortest distance between two locations is being calculated on a flat plane, and with the Great circle metric doing the same job on the surface of an ellipsoid, the latter produces an arc when projected onto a plane. Hence, the shortest distance across a plane map projection follows an arc, where the distance difference depends on projection method and map scale. Whatever metric is chosen, measurements are most often made on a horizontal projection of a three-dimensional world. Length and area may therefore be substantially lower than on a three dimensional surface, where error magnitude depends on landscape steepness. The length of a true curve is always longer than the length of its polyline or polygon representation, where error magnitude depends on the degree of geographic generalization.