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Spatial data - Introduction

76 important questions on Spatial data - Introduction

The simplified view of the real world adopteer by GIS is often termed a 'model'. What is a model?

A model is a synthesis of data which is used as a means of getting to grips with systems whose spatial scale or complexity might otherwise put them beyond our mental grasp

What are models containing ?

models are containing our ideas about how or why elements of the real world interact in a particular way.

What is a spatial model?

GIS populated with data and ideas about how these data interact is a spatial model.

Data fall into 2 categories primary and secundary, give some examples

primary -> counts of skiërs using a particular ski run are an example of primary data
secondary -> will have been collected by another individual or organisation, consumer surveys. secondary data sources are published and include maps, population census details and meteorological data.

What must be given to all spatial data in GIS ?

all spatial data must be given a mathematical spatial reference

Give an example of three modes or dimensies.

ski incident that took place in Three pines valley on 14 feb 2002, the three modes are :
-temporal - 15:30 hrs 14 feb 2002
-thematic - wet slab avalanche triggered by two off-piste skiërs and
-spatial
-Three pines valley, south facing slope

What are thematic maps ?

Thematic maps show data relating to a particular theme or topic, such as soil, geologie, geomorphology.

What are topographic maps ?

topographic maps contain a diverse set of data on different themes. Thus land use reliëf and cultural features may all appear on the same topographic map

What is the purpose of a map ?

the purpose of a map is to turn data into information that will be communicated to a third party.

The scale of a map ?

virtually all sources of spatial data, including maps are smaller than the reality they represent. scale gives an indication of how much smaller than reality a map is .

Scale can be expressed in 3 ways, which ones?

-ratio scale 1:50000
-verbal scale 1 cm representeer 50 m
-graphical scale 0-100km-200km

Traditionally, maps have used symbols to represent real-world features, Which one?

points, lines and areas

How can depth or heigth being added to the spatial data?

by adding a z-co-ordinate to the map

What are island polygons and what are adjacent polygons

island polygons occur in a variety of situations, not just in the case of real islands. for example, a woodland area may appear as an island within a field.

A map is a simplified presentation of a part of the real world. The real world is simplified in several ways give some examples

1. the three dimensions of the real world are reduceer to two dimensions
2.changes over time are ignored, resulting in a map which is a static snapshot of one specific moment in time.
3. the scale is reduceer
4. a lot of irrelevant details of the real world are ignoreer and not presented on the map

A simplified spatial presentation of the real world has to be developed. how is this processed called ?

spatial data modelling proces

When the term "model" is used within the context of GIS and spatial data modelling, it generally refers to?

a static description of the relative spatial positions of objects, phenomena and features in the real world. this type of model is also called descriptive. GIS is used more and more for predictive modelling.

What is the basic question to setup a data model in a GIS environment?

the basic question addressed is "how can we develop a suitable GIS database that representeer spatial phenomena from the real world with sufficient detail for the goal we have in mind.

What is the purpose of a GIS database?

1.which data to be included
2.how to represent your data
3.how to store the data
4.and the mathematical operations that have to be performed

What is a discrete perception?

include a town, road, animal and house but they can also be abstract constructs that are not directly observable, examples are zip-codes areas, telephone districten, a city centre

What is continuos perception?

a continous perception implies that a phenomenon occurs everywhere. exemples are background norse, daily solar irradiation

For the GIS analyse to make use of simple spatial entities (points, lines, and areas) it is necessary to locate them in two dimensions. give an example how to do this ?

think of an inflated ball, the ball is the globe, with the countries in their correct locaties, and shown as area entities with correct relative shares and sizes. imagine that you have to deflate the ball and lay it flat on a table whilst still displating all the countries. the only way to do this is to cut the beach ball into pièces. in doing this you would find that the distanties between countries will be altereer an their shape distorted.

What is the distinction between discrete and continuous perceptions ?

a classic example is hte concentration of a chemical in soil. you might argue that chemical molecules are discrete entities and that a soil concentration should therefore be considered discrete. however, a concentration is often considered a continuous phenemenon because the amount of chemical related to the amount of soil, resulting in omnipresence (within the soil).

You should not confuse the perception of a phenomenon in the real world with its representation on a map. give an example.

an example is soil type, which is typically considered a spatially continuous phenomenon because it occurs everywhere. however, soil type is often categorized in a limited number of classes such as clay and sand.

Is a paper site map of the headquarters of the Open Universiteit in Heerlen a descriptive or a predictive model?

It is a descriptive model, because it provides a static description of the university grounds.

Compare figure 1.6 on page 7 of the GIS text book with figure 3.2 on page 76; which picture represents a descriptive model, and why? Explain the difference between a descriptive and a predicitve model.

The figure in Chapter 1 describes a dynamic process, i.e. the steps taken to select a suitable location of a nuclear waste repository. The figure in Chapter 3 describes the spatial characteristics of a specific location, i.e. the Happy Valley ski resort. It is furthermore stated in the learning material that “a descriptive model describes a more or less static situation and a predictive model describes the process to predict future situations”. So the figure in Chapter 3 meets the characteristics of a descriptive model because it is static.

What is the difference between a paper map, a digital map and a GIS map?

The main difference is the flexibility. A paper map is much less flexible than a digital or GIS map. A digital or GIS map can be printed or processed using GIS technology. In this perspective, a digital or GIS map is preferable over a paper map.
The difference between a digital map and a GIS map is the number of layers. A digital map generally consists of one layer, whereas a GIS map can consist of multiple layers.

After a sand excavation close to the riverbed of the river Rhine, the area needs to be reconstructed in an economically valuable way. One of the options is to create a recreational area for swimming during summer and ice skating during winter. First an inventory has to take place whether there are enough potential users of such a recreational area. Which kind of maps do you need to get this insight?

At least maps with population density and transportation routes, which you can use to make an estimate of how many people may visit the area in relation to travelling time. You would also need some general data about the amount of swimmers and skaters in the population.

Decide whether the following phenomena are spatially discrete or continuous:
The concentration of Zinc (a heavy metal) in the soil.
The average annual rainfall.
The provinces and all major cities in The Netherlands.
The major transport routes from Rotterdam harbour to the destination of the goods.
The spatial distribution of mice in a nature area.

The concentration of Zinc (a heavy metal) in the soil: continuous.
The average annual rainfall: continuous.
The provinces and all major cities in The Netherlands: discrete (provinces and cities are discrete administrative areas).
The major transport routes from Rotterdam harbour to the destination of the goods: discrete (roads and other transport routes are discrete objects).
The spatial distribution of mice in a nature area: discrete. The mice themselves are discrete entities, although they are generally not individually represented on a map. It is more common to use mice density, which is a spatially continuous parameter.

Describe the relationship between scale and aggregation in your own words.

The smaller the scale, the more you will aggregate.

There are three types of projections which ones ?

a.cylindrical projection (light in a circular room analogy
b.azimuthal projection (light in a square room with flat walls analogie)
c.conic projection (light in a tepee analogy)

Several methods of spatial referencing exist, all can be grouped into 3 categories which one?

a.geographic co-ordinate systems
b.rectangular co-ordinate systems and
c.non-co-ordinate systems

Most of the spatial data available for use in GIS exist in 2-dimensional form. to make use of this data a referencing system is needed how is this called ?

a rectangular co-ordinates is required

There are 2 rectangular co-ordinates systems. mention them both ?

UK ordnance survey's national grid
Universal transfers mercator UTM

Spatial entities may be mobile think of ?

animals, cars; therefore any spatial reference they are tagged with will only represent their known location at a particular time

Spatial entities may change think of ?

rivers meander, roads can be relocated

A technique of field data collection which can be used for GIS is ?

satelilite navigation systems or GPS

How is the dutch national reference system called ?

Rijksdriehoekstelsel

Where is the rijksdriehoekstelsel central point ?

onze lieve vrouwetoren in amersfoort. this reference point is verticale projected onto the horizontal plane.

Why have amersfoort not zero coordinates ?

the coordinates are x = 155000.000m and y = 463000.000 m. these coordinates are expressed in a false system. the orientation of this false system is identical to that of the true system, but coordinate (0,0) is somewhere southeast of paris.

Explain the importance of map projections for users of GIS.

A map projections is method that is being used to project a 3D object (like the globe of the world) on a 2D surface. There are different types of map projects, e.g. a cylindrical, azimuthal or conic projection. Knowing the map projection of a map is important for a user of GIS because:

when overlaying maps (data analysis), these maps need to be in the same projection;
you need to know the map projection in order to translate map coordinates into geographic co-ordinates.

Why is a conic projection often used for European maps?

Projections always have distortions. These distortions are smallest in the areas where the projection plane touches the earth’s surface. Assuming that you want to show the North pole in the upper part of the 2D map, a cone will touch the earth’s surface around Europe (cylindrical and an azimuthal projections touch the earth’s surface around the meridian). Consequently,distortion for Europe is smallest using a conic projection.

Which parts of the world are distorted most in a cylindrical projection as presented in Figure 2.13a of the GIS text book?

The North and the South poles.

What is the difference between projections and reference systems?

In a rectangular co-ordinate system the coordinates refer to a location on the map, whereas in a geographic co-ordinate system the coordinates refer directly to a location on the earth’s surface. So, in a geographic co-ordinate system, the coordinate system is put over the earth’s surface and then projected (together with the earth’s surface) on a 2D plane. In a rectangular co-ordinate system, the earth’s surface is first projected on a 2D plane and then a rectangular co-ordinate system is put over the 2D plane.

What kind of reference system is the ZIP code system which is used by postal services?

It is a non-co-ordinate system.

What kind of spatial referencing systems are being used by GPS devices?

A GPS uses signals from GPS satellites to work out the exact location of the user on the earth’s surface. As a consequence, a GPS will essentially use a geographical co-ordinate system. Most modern GPSs contain different projection algorithms, enabling the translation of geographic co-ordinates into a multitude of different (geographical and rectangular) co-ordinate systems.

What is an aerial photograph ?

it is a snapshot of the earth at a particular instant in time. aerial photographs represent a versatile, relatively inexpensive and detailed data source for many GIS applications.

For GIS remotely sensed data offers many advantages. give some examples ?

1.Images are always available in digital form
2.there is the opportunity to process images or use different wavebands for the collection of data to highlight features of particular interest: water or vegetation.

What are Basic Spatial Unit (BSU's)?

is the smallest spatial entity to which data are encoded.

There are different ways to obtain digital spatial data. which one ?

-Primary data acquisition involves the direct measurement of geographical objects and phenomena. Data capture methods are available for both raster and vector data. Remote sensing and GPS are examples of primary data acquisition techniques.
-Secondary data acquisition is the process of creating raster and vector datasets from maps and other hardcopy data. Scanning,digitizing and photogrammetry are examples of secondary data acquisition techniques.

Remote sensing is being used to acquire information about environmental processes such as ?

agricultural crop growth, land cover changes, deforestation, vegetation dynamics, water quality dynamics, urban growth.

Where is remote sensing referring to ?

to the instrumentation, techniques and methods used to observe the surface of the earth at a distance remote from that surface.

When electromagnetic radiator hits an object it can be ?

transmitted, absorbeer or reflected

The moisture content of the soil causes higher or lower spectral reflectance ?

the spectral reflectance of a wet soil is lower than that of a dry soil

Depending on wavelength, sensors may vary in their sensitivity to electromagnetic radiation. distinction can be made ?

between panchromatisch sensors that record the total intensity or radiation falling on each pixel and multispectral sensors that record the radiation intensity at different spectral bands.

Give the steps of visual image interpretation

1.detection, the mere discovery that something is there
2.recognition and identification, something is recognised and identiteit as a known object by its shape,size and other visible properties
3.classification, the objects or entities get their specific name or term according to some classification system.
4.delineation, a boundary is drawn around the selected object or features and appropriate classificatie code is assigned

Define remote sensing in your own words.

To capture data for GIS of remote objects.
To sense objects without making contact.
To gather information about objects without making contact.

Visual image interpretation is the act of examining remotely sensed images for the purpose of ?

identyfing features and judging their significance.

Explain why GPS is a useful tool in the data stream.

A GPS can provide coordinates of ground elements which are recognisable on aerial images and therefore can be used to geo-reference that image. Also the GPS can be useful in field studies to pinpoint vegetation-quadrants for example.

What is the blocking effect?

Parts of the electromagnetic spectrum are filtered by the atmosphere and radiation of the earth surface in those wave-lengths cannot be captured by the sensors of satellites, i.e. the radiation is blocked.

Which scanners are not susceptible to cloud cover?

An important property of the long wavelengths used in the microwave region is that they are not susceptible to atmospheric scattering. As a result they can penetrate through cloud cover, haze and all but the heaviest rainfall. Consequently, active scanners that emit and sense long wavelengths are not susceptible to cloud cover. Examples include active scanners, like radar or laser emitting and receiving scanners.

N the overview of sensor types (syllabus paragraph B2.6 - The Sensor), the recording bands of different sensors are shown as numbered rectangles. Each rectangle represents one recorded value for the amount of reflectance within this band. Which sensor would you choose to discern water, sand and vegetation? Motivate your answer.

The Landsat TM has a band (5) at 1.6 µm and would be preferable.

Some sensors have a small band around (or just after) 0.8 µm, for example the CEASAR-CCD MSS. Why do you think this band is inserted? Hint: look at the spectral signatures in Figure B.7 of the syllabus (paragraph B2.5 Object - Radiation Interaction).

This band is inserted in the range of high reflection of vegetation, and in combination with other bands (like 1.6 µm) is very useful to sense if vegetation is present or not. Furthermore (not directly deductible from the figure), different vegetation types can be discerned because their reflection differs in this region (for example between pine trees (lower reflection) and deciduous trees (higher reflection).

What is a class?

a class is a set, collection, group or configuratie containing members regarded as having certain attributes or traits in common. in image classificatie, a class correspondent to a meaningful grouping of locaties that share a common characteristic . for example, forest, water and heat are all classes.

What are digital numbers ?

in a multispectral image, each pixel is characterized by a set of values or digital numbers. each DN reflects the intensity of the radiation within that particular spectral band that falls on that particular pixel.

The first step in an unsupervised classification is ....

to create clusters. a popular algoritme for defining clusters for unsupervised classificatie is the ISO data clustering algorithm. the ISO prefix stands for the Iterative Self Organizing a methode of performing clustering.

What is the input for classification?

the input to classification is a signature file that stores the multivariate statistics for each class or cluster of interest.

Once the signaturen files have been compiled, classification of the image pixels can start. How is this done ?

Each pixel will be assigned to one of the classes based on comparison of the pixel's DNs with those of the classes or clusters in the signature file. a pixel will be assignet to the class or cluster that most closely matches the DNs of the pixel.

Give the steps to perform an unsupervised classification:

1. load a multispectral image into the image analysis software
2. produce training samples from known locaties of desired classes
3. develop a signature file
4. view and edit the signature file if necessary
5. run the classification algorithm

Give the steps to perform an unsupervised clustering

1.load a multispectral image into the image analysis software
2.define the number of clusters to be created
3.run the clustering algoritme
4.view and edit the resulting signature file if necessary
5.run the classification algorithm

Explain the difference between supervised and unsupervised classification in your own words. Use the term training areas in the explanation.

In supervised classification, the definition of the spectral patterns (= interpretation) precedes the classification of pixels. The spectral patterns of the classes are defined by the interpreter. Around known land cover classes, so called training areas are delineated. The spectral patterns of these training areas are used to classify unknown pixels based on their spectral reflection pattern.

In an unsupervised classification, classification precedes the interpretation. First, an algorithm is applied which categorises the spectral patterns in classes. Subsequently, the interpreter has to assign a real world interpretation to the automatically assigned classes.

In the training stage of supervised classification, the image analyst collects spectral response patternsof classes he or she wants to map, e.g. water, sand, forest, etc. Why are these spectral response patterns needed?

The spectral response patterns are used to compare the spectral pattern of an unclassified pixel and with the typical spectral response pattern of the classes that are to be mapped (signatures). In this way, unknown pixels can be classified based on their resemblance with these signatures.

What are the basic steps in supervised classification? Which step is different in unsupervised classification?

Stages of supervised classification:

Training stage
Classification stage
Output stage.

In unsupervised classification there is no training stage. It starts with the classification stage (i.e. choosing a classification algorithm and defining criteria for classification such as the number of classes or class thresholds). Signatures are generated automatically in unsupervised classification.

Give different scales of measurement ?

-nominal scale; numbers are used to establish identity. in happy valley, numbers numbers on a nominale scale include telephone numbers or ski pass codes.
-the numbers in an ordinaal scale establish order. location in a ski lift queue is an example.
-on an interval scale the difference between numbers is meaningful but the scale does not have a real origin. negative numbers are also possible on an interval scale
-on a ratio scale measurements can have an absolute or real zero, and the difference between the numbers is significant

What are the sub-processes of abstraction?

reduction, (thematic) classification and (spatial) aggregation

What is spatial aggregation?

Process of joining multiple,adjacent spatial entities into one spatial entity

The question on the page originate from the summary of the following study material:

An introduction to geographical information systems | 9780273722595 | Ian Heywood, et al

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