GIS review

Explain the UTM coordinate system

...This system is a specialized application of the transverse Mercator projection which is both cylindrical and conformal. It divides the world into 60 numbered zones, both north and south, separated by the equator. Each zone spans six degrees of longitude and has its own central meridian. This system was adopted by the US Army Map Service in 1947 for their use in worldwide mapping and continues to be used worldwide. Florida falls into UTM zones 16 and 17. When using the UTM system, linear parameters are established. The origin of each UTM zone is the intersection of its central meridian and the equator, and the parameters are applied to this origin to make it convenient to work with making all x and y values positive, or reducing their range. The first parameter is the false easting - a linear value applied to the origin of the x-coordinates - or the central meridian. The second parameter is the false northing - a linear value applied to the origin of the y-coordinates - or the equator. The final parameter used in a UTM grid system is a fixed parameter called the scale factor. The scale factor is a unitless value (usually less than one) that is applied to the center point or line of a map projection to reduce the distortion of the projection in the area of interest. The value of the scale factor for the UTM system is 0.9996

Describe the 4 types of map projections by the preserved property.

A Conformal projection preserves local angles and shapes. An Equivalent projection represents areas in correct relative size. An Equidistant projection maintains consistency of scale along certain lines. An Azimuthal projection retains certain accurate directions.

Explain how a UTM zone is defined in terms of its central meridian, standard meridian, and scale factor.

A UTM zone is mapped onto a secant case transverse Mercator projection, with a scale factor of 0.9996 at the central meridian. The standard meridians are 180 kilometers to the east and west of the central meridian.

central meridian

A central meridian is a meridian that passes through the center of a projection. The central meridian is often a straight line that is an axis of symmetry of the projection.

Define Relational Database.

A collection of tables in which tables are connected by keys.

UTM

A coordinate system based on the Transverse Mercator projection, developed in the 1940s. The globe is divided into 60 individual 6-degree wide longitudinal strips extending from 80S to 84N The central meridian is assigned a value of 500,00m to avoid negative easting coordinates. This places the origin outside the zone at 500km west of the central meridian. The origin is called a false origin and the easting coordinates are referred to as false easting In the Northern hemisphere, the equator is the origin for northing coordinates In the Southern hemisphere, the equator is assigned a false northing of 10,000,000m, again to avoid negative northing coordinates.

Describe the 3 types of map projections by the projection or developable surface.

A cylindrical projection uses a cylinder as the projection or developable surface A conic projection uses a cone An azimuthal projection uses a plane.

Database

A database is a collection of persistent data which is formally defined and centrally controlled for use in a computer.

Datum

A geodetic datum is a set of values used to define a specific geodetic system to describe the size and shape of the ellipsoid used and the origin and orientation of the coordinate systems used.

What is datum?

A mathematical model of the Earth, which serves as the reference base for calculating the geographic coordinates of a location.

Ordinal

A measurement scale in which scores indicate rank order like fire risk

georelational data model

A model that represents geographic features as an interrelated set of spatial and attribute data. It is the fundamental data model used in coverages.

Explain the difference between the standard line and the central line.

A standard line refers to the line of tangency between the projection surface and the reference globe. In other words, there is no projection distortion along a standard line. The central lines (i.e., the central parallel and meridian) define the center of a map projection.

Data acquisition

Acquire Data spatial data input attribute data input linking spatial and attribute data

Reference Maps

Base maps, a record of what is there, general purpose

Basic map elements

Border, Orientation, Legend, Title, Scale,

Data Structures of Raster

Cell by Cell - stores strings Run - Length encoding - records by row and group Quad tree encoding. - divides grid into quadrants recursivley until single cell is reached

Map Layout

Clarity, order (map logic), balance, contrast, unity and harmony.

Abstraction of real world

Conceptual process of reducing the real world into themes, in an urban setting the real world might be simplified to building, roads, railways, garden, open spaces, etc. A paper MAP is ABSTRACTION.

topology Model

Concerned with relationships between spatial objects, but not their physical shape. Two most common are adjacency (do they share a common boundary) and containment (is a residence withing a school zone)

metadata

Data about data. coverage, data quality, data currency as well as information on who created the data and how it should be interpreted.

advantages of Database

Data is easily shared data is permanent easily accessed through search easily used by a computer to locate data quickly

Data quality

Date of collection method of collection scale resolution coordinate system and projection coverage completeness condition , readability and convenience. availability.

Rater Data model

Divides the study area into a regular set of grid cells. Generate by laying the grid over themes abstracted from reality coding each cell with a single attribute structuring the codes so you computer can store them.

Explain the importance of map projection.

First, a map projection allows us to use 2 dimensional maps, either paper or digital, instead of a globe. Second, a map projection allows us to work with plane or projected coordinates rather than longitude and latitude values. Computations with geographic coordinates are more complex and yield less accurate distance measurements.

AGD66 and GDA94 differences

GDA94 replaced AGD66 in 2000, thus moving from a local reference ellipsoid (ANS for AGD66) to a global reference ellipsoid (GRS80 for GDA94). GDA94 is a geocentric datum and compatible with GPS data. The Australian Geodetic Datum 1966 (AGD66) is based on the Australian National Spheroid (ANS) reference ellipsoid with its origin at the Johnston Geodetic Station in the Northern Territory. This datum was designed to be a best fit for the Australian region. The centre of the ANS does not coincide with the centre of the Earth but lies about 200m from it.

What is GIS?

Geographic Information Systems is a computer system for capturing, storing, querying, analyzing and displaying geospatial data.

Define geometries and attributes as the two components of GIS data.

Geometric data describe the locations of spatial features, which may be discrete or continuous. Attribute data describe the characteristics of spatial features.

Origin

Grid extent and cell resolution.

Nominal

Groups that can't be compared like postcodes or text

What is Topology?

It expresses the spatial relationships between features,

Latitude and Longitude

Latitude- parallel lines which run east and west and measure distance north and south of the equator. Longitude- "meridians" which run north and south and measure distance east and west of the prime meridian. , A geographic coordinate system.

Map projections

Most projections are combinations of the following characteristics: the shape of the projection plane, the aspect of the projection plane, the points or lines of tangency or secancy and the location of the false illumination source.

Data classification

Natural breaks, equal interval, quantile, standard deviation.

Applications of GIS

Natural resource management, environmental applications, government applications.

Ratio data

Numbers are in order, have an equal value in between them, and zero represents an absence of something. Ex: number of children or number of cars.

Discrete object themes

Objects with finite boundary, usually represented by the vector model.

Building a database.

Plan project requirements and scope the range, type and quality of data Identify and collect appropriate information sources. Determine the input method to be used and prepare the data accordingly. Will you be creating vector, raster or aspatial data? Data input to transform the data to digital format. Methods to capture data are described in detail later in this module and include scanning, digitising and keyboard entry. Preprocessing steps - these are the procedures used to convert a dataset into form suitable for permanent storage within the GIS and database and include digitisation, rectification, error checking, topology building and linking spatial and attribute data. Step 1 is critical so that budget, time and project requirements are determined prior to beginning data entry. Otherwise too much time can be spent on data collection of irrelevant items.

Benefits of Topology

Processes are faster, No duplication, Error correction and detection.

Database Models

Relational (files containing records, connected together by key attributes, most popular for GIS, SQL is used to access data) Object orientated

Joins and relates

Relationships, one to one, one to many, or many to many, Join lets you append additional data to a layers attribute table using comon fields, Relate lets you associate data with a layers attribute table, but the data isn't appended. relate is useful for one to many or many to many.

Describe the 3 levels of approximation of the shape and size of the Earth for GIS applications.

SPHERE, SPHEROID/ELLIPSOID, GEOID

Drawbacks of Topology

Some simple operations are slow because of complexity. It requires additional files to store the spatial relationships.

Three vector models

Spaghetti & topological models (both varients of the georelational model) & object based model

Thematic maps

Special purpose maps, emphasis on a specific theme.

Spagettie model

Stores features as independent objects, unrelated to each other.

Different spatial resolution

Such as using a state boundary digitised as 1:1,000,000 on a large-scale topo map.

DBMS

System used to manage a database

Australian Geodetic Datum 1966 (AGD66)

The Australian Geodetic Datum 1966 (AGD66) is based on the Australian National Spheroid (ANS) reference ellipsoid with its origin at the Johnston Geodetic Station in the Northern Territory. This datum was designed to be a best fit for the Australian region. The centre of the ANS does not coincide with the centre of the Earth but lies about 200m from it.

Aspect of the projection plane

The aspect of the projection plane can be normal, transverse or oblique. A normal aspect has the axis of the plane parallel to the axis of the Earth. A transverse aspect has the axis of the plane perpendicular to the axis of the Earth and an oblique aspect is any other orientation.

Define geospatial data.

The data that describes both the LOCATION and CHARACTERISTICS of spatial features (such as roads, land parcels, and vegetation stands on the Earth's surface.)

Vector Data Model: Explain the difference between the georelational data model and the object-based data model.

The georelational data model uses a split system to store spatial data and attribute data. The object-based data model stores spatial data and attribute data in a single system.

False illumination source

The location of the false illumination source can be standard or gnomonic (the centre of the Earth), stereographic (at the pole opposite the plane of projection) or orthographic (at infinity)

Define Geographic coordinate system.

The location reference system for spatial features on the Earth's surface using latitude and longitude.

Globe

The only kind of map that does not distort shape, distance, area or direction.

Tangency and secancy

The points or lines of tangency or secancy are the only places where no distortion occurs on a map, and distortion increase with distance from them. A XXXXXXX projection touches the surface of the Earth and a XXXXX projection intersects or slices through the surface of the Earth

Define Projection.

The process of transforming from a geographic coordinate system to a projected coordinate system. Can also be reprojected onto another coordinate system.

How is the scale factor related to the principal scale?

The scale factor is defined as the ratio of the local scale to the principal scale. In other words, the scale factor is the normalized local scale. Will be 1 along the standard line and more distorted away from the line.

Classification by properties preserved

There are four properties, of which only one or two can be preserved in any single projection. Conformal A conformal projection preserves shape by constant scale Equal area An equal area projection preserves sizes Equidistant An equidistant projection preserves distances Azimuthal An azimuthal projection preserves direction - a constant bearing is a straight line

Developable surface

Three common shapes are azimuthal, cylindrical and conical An azimuthal projection projects directly onto a flat planar surface. A cylindrical projection projects onto a rolled cylinder and a conical projection projects onto a rolled cone.

Name two tools or techniques for vector data analysis.

Tools for vector data analysis include buffering, overlay, distance measurement, spatial statistics, and map manipulation.

Topology advantages and disadvangates

Topology is concerned with relationships between spatial objects, but not their physical shape. It is a technique used to record and manipulate the logical relationships of spatial features. Advantages. No duplication. There is no repetition of spatial coordinates between one polygon and another, so repeated lines are eliminated. This reduces redundancy and improves integrity of the data. Error detection and correction. Topology allows for error detection, such as double digitising, sliver polygons and unclosed polygons. These can all be easily detected using defined topology Disadvantages Some simple operations such as graphic display are slow and cumbersome due to the complex data structure Topology requires additional files to store the spatial relationships

The Object based model

Treats spatial data as objects with associated properties and methods.

What is TIN?

Triangulated Irregular Network.

Overlays

Union, intersect and Clip

Name two commonly used projected coordinate systems that are based on the transverse Mercator projection.

Universal Transverse Mercator (UTM) grid system State Plane Coordinate (SPC) system.

Discretisation

Using a grid to create simple manageable discrete units which a computer can process.

Explain the difference between vector data and raster data.

Vector data use points and their x-, y-coordinates to represent spatial features of points, lines, and areas. Raster data use a grid and grid cells to represent the spatial variation of a feature (such as elevation or precipitation.)

GIS Analysis Functions

Vector: Measurement, queries, buffering, reclassification, overlay operations Raster: Neighbourhood functions, reclassification, overlay Advanced spatial analysis: Network analysis, Visibility analysis (viewshed), terrain analysis, interpolation.

Methods for deciding cell assignment in raster model

Winner takes all Assigned dominance. Edge Cell assignment.

Error

a general term for a mistake

false northing

a measurement made north (or south) of an imaginary line such as used in measuring UTM northings in the southern hemisphere, it is assigned a false northing of 10,000,000m to avoid negative northing coodinates.

Affine Transformations

apply to both vector and raster data and include rotation, scaling, skey and transformation, or combinations of these.

Continuous object themes

complex surfaces, with no obvious defined boundary. Like a volcano. usually represented by the raster model.

geospatial data

data that describes where something is, as well as what something is.

attribute

defines "what" features are in regards to spatial data. An attribute in non-spatial characteristics such as labels, categories, numbers, dates or standardised values.

GIS components

hardware, software, data, people and infrastructure.

Accuracy

how much a map or database approximates reality

raster data analysis.

includes local, neighborhood, zonal, and global operations.

Spatial and attribute information

information that is stored via spatial and aspatial data in files, which are linked together. stored as vector and raster.

Interval

like degrees celsius. addition and subtraction are valid. but multiplication is not.

Vector analysis operations

measurement queries buffering reclassification overlay operations

Raster analysis operations

neighbourhood functions reclassification overlay

Cartesian coodinates

planar coordinates used for small areas.

Varying accuracy

some data collected by GPS and some by previous digitising from maps of unknown generalisation. Some may have been stretched from previous geometry during georeferencing.

Rubber sheeting

stretches and distorts pre-existing vector data to move vertices and nodes to knows locations. It preserves the topological structure within the data.

Precision

the level of measurement and exactness of discription in a GIS database.

Different coordinates

under different Earth model approximations, the same spot on the Earth will be represented by different values for its coordinates (see Module 6).

Different temporal relevance

using old images of a flood extent in your incident management system, or using an old air photo of a city before all the suburb development in a city mapping project.

false easting

value added to x to ensure no negative values, 500,000 is central meridian

Quantitative maps

visual variables ex. size, pattern texture, gray tone, color lightness, color saturation ---- shows how much of something exists at some location (how many, large, wide, fast, deep things are)

Scale

with spatial models, complex shapes are simplified, Scale is fundamental for how features are generalized. Scale of a map is the ratio between distances on the map and the corresponding distances in the real world.

Dimensionality

zero = point, one = line, two = polygon, 2.5 = one z value only, 3 = any z-y-z