Tenta Plugg Past Paper PDF

**Tenta Plugg** march 25, 2014 **1. In GIS, geographic problems are assessed.** **a. What is meant with a geographic problem -- please define?** *Geographic problems involve an aspect of location, either in the information used for solving these problems or in the solutions themselves.* "Proble...

**Tenta Plugg** march 25, 2014 **1. In GIS, geographic problems are assessed.** **a. What is meant with a geographic problem -- please define?** *Geographic problems involve an aspect of location, either in the information used for solving these problems or in the solutions themselves.* "Problems that utilise geographic position for their solution are called geographic problems." Examples of geographical problems: Forest management, precision farming, finding your way in an unfamiliar city **b. With so many problems being geographic, there is a need to categorize them. Mention at least three methods for categorizing geographic problems.** Scale, Intent/purpose and time-scale **c. For each of the above methods, list the associated categories and provide examples within each category.** *Scale (geographic detail) - defines the level of detail in which the problem is looked at. Here there are 4 different categories:* - - - - *Purpose/Intent -* - - *Time-scale -* - - - **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?** A geodetic datum links a position in time and space, with a descriptive property called attribute. Geographic attributes has a value. "Geographic data is built up from atomic elements. At its most primitive, an atom of geographic data (datum) links a position (in space and time) with some descriptive property. The descriptive property of a geographic object is called its attribute. Attributes have a value. Geographic attributes are classified by: - - - - - They are graded with ranking, equidistance and absolute zero. **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?** Tessellation and constant-values **b. Exactly how do they simplify geographic reality?** [Tessellation (or Spatial averaging by pixel)] simplefies by deciding the size of (dpi: pixel density). We can either simplify or add more detail depending on the pixel density. More detail, more pixels and less detail, less pixels. Constant-value can be used to simplify large areas that contain the same, constant or similar attributes to one. "Utilizing the fact that many attributes remain constant over large areas. For example the oceans could be simplified to only one value, since it takes up ⅔ of our world. We can therefore represent areas that have similar or shared attributes and therefore reduce the amount of information." **c. What are the two corresponding methods of representing geographic data in a computer called.** Raster and Vector **d. In the two respective methods of digital representation, exactly how is the amount of information for representing geographic objects regulated?** In raster the information is regulated by pixel size and for vectors the amount of points the object is given. the more points or more pixels, the more detailed an object. **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**. I would represent the well defined lake that never changes extent, with vectors. for the fuzzy representation the raster would be better suited. categories for the fuzzy representation and raster method would be: 1. 2. 3. 4. **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?** A cylindrical projection is like a paper being wrapped around the earth, forming a cylinder. This to make an analog map. That it is transversal means that the cylinder touches the north and south pole. While for the normal cylindrical it touches the equator / meridian. Secant projection is used to minimize the scaling error, by alluding the paper to cut through the ellipsoid surface. This to minimize distortion. The central meridian relates to this due to the "paper" touching the earth on this line (meridian). "Secant projection models minimise average scale error by allowing the paper to cut through the ellipsoid surface" "Secant projections try to minimise distortion by allowing the paper to cut through the surface, so that the scale can be both greater and less than 1" "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 3 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?** The terrain map contains land-cover, topography, infrastructures, urban structure, hydrology and so on. In a non-arid region the referential skeleton can be things like water bodies (especially for a post-glacial land like Sweden, with alot of water), urban structures, land-covers etc. Anything that can be used for orientation. The terrain map is typically used for geographic analysis, physical planning, geographic orientation, geographic presentation, etc. "Where water is abundant, hydrology typically constitutes the map skeleton" **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]: LANDSAT- infrared sensor, that is depicting vegetation. Digital cameras- mounted on airplane to take orthophotos uses the sun as light source, hench passive [Active sensors: ] Radar (mounted on airplanes) - for depicting elevation Sonar - (mounted on ships) - for seafloor elevation Sends out its own signals that bounce back and give information about the elevation. hence active. **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. 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 ChatGPT: ### **1. Projection Distortion** - - - ### **2. Ellipsoidal Shape of the Earth** - - - ### **3. Geoid Undulations (Height Variation)** - - - These sources of error reflect different aspects of the Earth\'s complexity and how they impact measurements when transitioning from a 3D model to a 2D representation on a map xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx may 2014 **1. Please define a datum of geographic information. Also define a geographic problem. Provide at least three examples of geographic problems.** A geographic datum contains a position, together with an attribute value. The position is given in the geodetic datum and the attribute value indicates the geographic content at the position. "problems that utilise geographic position for their solution are called geographic problems" Three examples of geographic problems are: Precision farming (to mint-max crops growth at the same time decreasing over use of fertilizers). Forest management (where to cut, replant, find the best places to put roads etc). Finding your way in an unfamiliar place. **2. Present at least two advantages and two disadvantages with each method for representing geographic objects (raster, vector) in a GIS** "Advantages with raster data are simple data structure, can store continuous surface data such as temperature, ability to represent fuzzy objects like wetland lakes and mountains. Examples of disadvantages are the lack of topology and their relatively large storage requirement. Advantages with vector data are exact geometry, ability to handle multiple attributes for each object, and a well-defined topology. Classical disadvantages are their unreasonable precision, their algorithmic complexity, and their inability to represent continuous phenomena" **3. A "spatiotemporal" scenario may be conceptualised as spatial change over a period of time. Can you suggest how to catch such change with a GIS?** I would use the raster method to show change. Because we are dealing with continuous data and fuzzy edges. A way of catching it is to gather data during the different time changes (if it is every month, year, seasonal or other) of need. That via temporal snapshots (Temporal data is simply data that represents a state in time and snapshots are images. Time/visual content). It shows the degree of change. **4. The geoid is a rather mysterious surface with a mean radius that coincides with WGS84, but with a surface that, at every position, is orthogonal to Earth's gravity field (and is therefore irregularly shaped). How may the characteristics of the geoid be utilised when a local geodetic datum is defined? Please use the phrase "local ellipsoid" in your answer and illustrate with some extremely situated region (as compared with the global scenario)** The geoid provides a local gravity reference as well as a smooth approximation of Earth's surface. In order to catch the local gravity reference, a local ellipsoid is used to approximate the (local) curvature of the geoid. When objects situated at Earth's surface are projected onto the local ellipsoid, the resulting surface is mathematically well-defined while the gravity reference as well as the relation to the global ellipsoid is maintained. **5. The advantage of using a secant map projection, as compared with a tangential projection, is easily expressed. What is it?** **Please provide an example on an international geodetic datum that utilizes a transversal secant cylinder as projection model, and where this cylinder is being rotated sixty steps in order to cover the circumference of the Earth.** The advantage is that a secant map projection minimizes the scale error, due to allowing the paper to cut through the ellipsoid. it minimizes the distortion. an example of international geodetic datum that uses the secant cylinder as an projection model is: (UTM) Universal Transverse Mercator Answer:"Lesser average scaling error. Universal Transverse Mercator (UTM)." **6. How many GPS technologies can you list? Please provide names and technological** **characteristic. The maximum number of technologies is five.** **What is the benefit of real-time GPS as compared with GPS that does not operate in real-time? What is the main benefit of a GPS that does not operate in real-time?** " absolute code in real-time (absolute GPS); relative code in real-time (differential GPS); relative phase-shift with post-calculation (statistical GPS); relative phase-shift in real-time (single station RTK); compensated relative phase-shift in real-time (network RTK). Real-time GPS operates while being moved around, which may be utilised for navigation. Non real-time GPS (statistical GPS) requires stationarity for a long enough period of time to calculate a highly accurate position (post-centimetre precision). **7. What is ortho-correction good for, and how is it done?** "What is ortho correction? What is orthorectification? Orthorectification is the process of removing image distortions or displacements caused by sensor tilt and topographic relief" "With most sensors being close to point-shaped in comparison with the area of land that they sense, a slight shift of perspective is introduced in the sensed image. The reason for this is the shifting distance between sensor and the horizontal plane below, where the distance is minimal in zenith and increases towards the peripheral image. The result is a convex image that may be ortho-corrected via projection onto a concave surface. [The ortho-corrected image does not contain any shift of perspective], and is hence "seen from zenith" [regardless of the position]. The problem with shifting perspective across the image decreases with the distance between sensor and Earth" **ChatGPT:** **"Ortho-correction** (or **orthorectification**) is a process used in remote sensing and geospatial imaging to correct distortions in aerial or satellite images caused by the camera\'s perspective, topography, or the Earth\'s curvature. The goal is to produce an image where the scale is uniform, and the image is geometrically accurate, meaning that it represents the Earth\'s surface as if viewed from directly above. ### **What is ortho-correction good for?** 1. 2. 3. 4. ### **How is ortho-correction done?** Ortho-correction is performed through several steps: 1. 2. 3. - - 4. 5. ### **Summary:** Ortho-correction is important for creating geometrically accurate, scale-consistent images from aerial or satellite imagery. It is particularly useful in mapping, environmental monitoring, and any application requiring accurate spatial measurements. The process involves identifying distortions, using reference data (like DEMs and GCPs), and applying mathematical corrections to produce an accurate, corrected image. " **8. What is the difference between a formal map and a map-like depiction?** **What is the difference between maps and charts?** **What is the difference between reference maps and thematic maps?** **Provide an example regarding each of the six map-types mentioned above.** A [formal map] is made in accordance with cartographic conventions (assigned symbols, color, meanings etc) and where the map contains geographical references. Some examples are terrain maps, road maps etc. [The map-like depiction] is used for analysing, visualising and editing. It has no formal claims. One example is cartograms over subways or buslines. They have no distance or exact location you can reference, but shows stops, somewhat of a direction etc. [Maps] are used for a terrestrial plain (example earth\'s surface) while *charts* are used out on maritime areas (the seas or large lakes). [Reference maps] depict the land with the attributes required for recognition (such as lakes, mountains, cities, buildings, infrastructure etc) [Thematic maps] focus on specific attributes (example: the extent of malaria cases in the western Sudan). **9. Provide a brief account for the principles that govern invers-distance-weighted interpolation. In the invers-distance-weighted context, what is an isotropic interpolation kernel?** "Most interpolation methods rest on the assumption that a continuous field has been observed in a finite number of localities, and that some spatial correlation structure may be utilized to restore continuity. In the case of inverse distance weighting, the value of the interpolation kernel is determined by a linear combination of all surrounding observations weighted inversely proportional to their distance (from the kernel). In isotropic interpolation, the observations are weighted irrespective their angular direction (from the kernel), whereas isotropic an interpolation assumes a direction-dependent interpolation kernel" "**ChatGBT:** **Inverse Distance Weighting (IDW)** IDW is a method to predict values at unknown points based on nearby known points. The closer a known point is to the unknown point, the more influence it has on the predicted value.The formula gives more weight to closer points and less weight to distant points. **Isotropic Kernel in IDW** An isotropic interpolation kernel means that the influence of each nearby point depends only on how far it is, not on the direction. The influence fades the same way in all directions---like ripples in water. This contrasts with an anisotropic kernel, where the influence could change based on direction (e.g., closer in one direction, farther in another). In simple terms: an isotropic kernel means the influence of nearby points is the same no matter which direction you\'re looking" **Interpolation** is the process of estimating unknown values between known data points. It's commonly used when you have a set of data points (like measurements or observations), but need to predict values at locations or times where you don't have data. In simpler terms: [Interpolation fills in the gaps between known values]. If you know the value of something at one point (e.g., at 2 PM) and at another point (e.g., at 4 PM), interpolation can help you estimate the value at a point in between (e.g., 3 PM). Example: Imagine you have the following temperature data: At 1 PM, the temperature is 20°C. At 3 PM, the temperature is 25°C. If you want to estimate the temperature at 2 PM (between 1 PM and 3 PM), you would interpolate to find the value. Types of Interpolation: **Linear Interpolation**: Estimates values by drawing straight lines between known points. **Polynomial Interpolation**: Uses higher-order curves to estimate values. **Spatial Interpolation**: Estimates values at unmeasured locations based on nearby measured values, such as in geography or environmental science (e.g., using Inverse Distance Weighting (IDW)) In simple terms, a **kernel** is a function that defines how data points interact with each other in a mathematical model or algorithm. It helps to weigh or influence the importance of different data points based on certain properties, like distance or direction. ### **In the context of interpolation:** - - - ### **Common Types of Kernels:** 1. 2. **10. You're employed by the national traffic authorities to plan the construction of a new highway in the east-west direction through mid-Sweden. The planning procedure is managed with a digital GIS; what would your main considerations be? What criteria would govern your choice of route? What data sources would you require? What overall GIS methodologies? What main obstacles would you anticipate?** "A large number of factors must be considered and weighted together; existing roads, urban centers, nature reserves, topography and hydrography, political strategies, etc., etc. All factors need to be superimposed on a map, and the new route sought in the resulting topology. The data sources should cover the decision-factors with thematic information, and be stored in a project map-base for storage and analysis. The main obstacles are probably political, where public opinions must be weighted into a comparison of the gains and losses associated with the new road" xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx **4.** **The geoid is a rather strange surface that aligns to the WGS84 radius at average, but retains perpendicular to gravity at every location. This introduces local anomalies as compared with WGS84; how can this unevenness be utilized for the creation of a local geodetic datum? Please use the term "local ellipsoid" in your answer and illustrate it with a simple drawing.** **Chat GPT:**\ The geoid is a reference surface used in geodesy, representing the mean sea level across the world, where gravity is perpendicular to the surface at every point. In contrast, the WGS84 ellipsoid is a mathematical model that approximates the Earth\'s shape but does not account for local variations in gravity or topography, which is why the geoid and WGS84 ellipsoid generally do not match perfectly. The differences between the geoid and the WGS84 ellipsoid, which can vary from region to region, are caused by local anomalies in gravity, such as variations in Earth\'s mass distribution and the Earth\'s topography (mountains, valleys, etc.). To create a **local geodetic datum**, we can utilize the **geoid undulation** (the vertical distance between the geoid and the WGS84 ellipsoid) in a region to define a **local ellipsoid**. This ellipsoid would be tailored to best fit the region\'s specific gravity and topographic features, ensuring that the local ellipsoid approximates the geoid better than the WGS84 ellipsoid. In other words, the local ellipsoid would be adjusted to align more closely with the mean sea level or geoid in that particular region, minimizing the vertical differences between the geoid and the ellipsoid. Here's how this works: 1. 2. 3. 4. ### **Illustration:** Imagine an idealized Earth with the WGS84 ellipsoid and geoid: - - Now, to create a **local ellipsoid**: - This would be a simplified version of how a local datum is created by using the geoid to define a local ellipsoid. I\'ll create a simple drawing to illustrate this concept: 1. 2. 3. Let me show you the drawing. It seems that the image request didn\'t process. Let me instead describe the drawing concept: 1. 2. 3. This visual representation would help demonstrate how the local ellipsoid adapts to fit local gravitational anomalies, providing better geodetic measurements for that specific region. If you\'d like, I can help you create a simple graphic in a different way!