EAS 221: Midterm Content

What is remote sensing?

The process of collecting and interpreting info about the Earth's surface or environment from a distance

What is spatial data?

Data that has location and dimension; answers the question "where is it?"

What is attribute data?

Non-spatial data of vector and raster data; answers the question "what is it?"

What is a Geographic Information System (GIS)?

A system that intregrates hard/software and data for capturing, managing, analyzing, and displaying all forms of geography referenced imaging; it also analyses vector and raster data in separate layers

What is vector data?

Points, line, polygons

What is raster data?

A matrix of cells organized into rows and columns where each cell contains a value

What are discrete elements and/or a discrete object view?

The world is empty, except where occupied by objects with defined locations and boundaries; vector data we choose to include will be represented

What are continuous elements and/or a continuous field view?

The world is full/completely covered and represents geographic space through a finite number of variables, each one defined at every possible position

What 2 issues are unavoidable when making a map?

Most maps are distortions of reality to some degree and use symbols that are proportionally too large (and therefore are selectively incomplete)

What is the definition of scale?

A map's representative fraction/ratio

What are the 2 common scales used by National topographic series maps in Canada?

1:250 000 (1 cm = 2.5 km) and 1:50 000 (1 cm = 0.5 km)

What does it mean for a map to be small scale?

The map shows less detail due to having a smaller representative ratio/scale

What does it mean for a map to be large scale?

The map shows more detail due to having a larger representaive ratio/scale

How does spatial generalization change with map scale?

There is more generalization as scale decreases (the area represented is larger)

What does a general purpose or reference map show?

Shows very general geographic features or boundaries of sorts

What do thematic maps show?

Shows a general distribution or trend over an area; for mapping data

What are chloropleth maps and what do they show?

A type of thematic map that is spatially extensive or intensive

What does it mean for a map to be spatially extensive?

The data it represents is true for the entire area (e.g. population of Alberta)

What does it mean for a map to be spatially intensive?

The data it represents is variable over an area (e.g. population density)

What are isopleth maps and what do they show?

A type of thematic map that has lines that connect points of equal attributes or value (e.g. elevation); it is used to represent rasters with vectors and generalizes data points

What is an isobath map?

A type of isopleth map that represents depths

What is an isobar map?

A type of isopleth map that represents heights

What is an isohyet map?

A type of isopleth map that represents precipitation levels

What are dot maps and what do they show?

A type of thematic map that has symbols that represent the presence of some mapped feature; can use a continuous colour scale to show frequency/intensity

What are graduated symbol maps and what do they show?

A type of thematic map that has symbols of various sizes to represent a range of values

What are the 2 main challenges of thematic mapping?

Appropriately mapping spatial phenomena/aggregation and dividing attribute data properly

What kind of data does a histogram represent?

Continuous data

What does it mean to make data equal-interval?

Split the data into equal ranges

What is the purpose of using natural (Jenks) breaks to vizualize data?

Goal is the minimize variation within classes and maximize variation between classes

How does natural (Jenks) breaks create separate classes?

Utilizes naturally occuring gaps in the dataset

What does a projected coordinate system do?

Converts locations on the earth's curved surface onto a flat surface

What are the 3 types of surfaces that a coordinate system can be projected onto?

Clyindrical, conical, and azimuthal

What are the 3 possible developable surface aspects?

Normal (upright from N to S), transverse (sideways, perpendicular to Earth's axis), and oblique (anything else)

What does a developable surface refer to?

The flat shape coordinates get projected onto

What does developable point of secancy refer to?

How a developable surface makes contact with the Earth's ellipsoid

What are the 2 possible developable points of secancy?

Tangent (just touching) and secant (intersecting)

What is the relationship between distance from the developable surfaces' point(s) of conatct with the Earth's surface?

The larger the distance between the developable surface and the Earth's surface means more distortion

What is the only way to have zero distortion in a map?

Remain in 3D

What are the 4 categories of projections?

Conformal, equal-area, equidistant, and compromise

What does a conformal projection do?

Preserves the shape of small areas

What does an equal-area projection do?

Preserves area

What does an equidistant projection do?

Preserves distance between certain points

What does a compromise projection do?

Attempts to balance different properties (shapes, area, and distance)

What kind of projection category does the Mercator Projection fall into?

Conformal, normal cylindrical projection

Where does the distortion on the Mercator Projection occur and what properties are preserved?

Distortions occur at the poles and shape is preserved but size is not

What is a key feature of the grid system of the Mercator Projection?

Spacing of parallels (latitudinal lines; E-W lines) increases towards the poles

What type of surface is a gnomonic projection projected onto?

Azimuthal

What are great circles?

Straight lines on gnomonic projections

What industry uses great circles for navigation?

Aviation

What is the Lambert Conformal Conic projection good for?

Large east-west extents in mid latitude and latitude range is less than 30 degrees; mainly used for mapping countries

What are the 4 considerations you need to make before choosing a projection type to work with?

Does your employer dictate projection type, projection type may matter for laerge scale areas, the application of the map, and what options your GIS software has

What is georeferencing (aka geocoding/geolocating)?

The process of defining position with repsect to a reference frame

What are the 3 requirements of georeferencing?

Uniqueness, interoperability, and persistance

What does uniqueness refer to as a requirement of georeferencing?

Each position is unique

What does interoperability refer to as a requirement of georeferencing?

The ability to exchange and make use of info

What does persistance refer to as a requirement of georeferencing?

The ability of the system to maintain the same georeference overtime, which is essential for accuracy

What is metric georeferencing?

Using coordinate systems to define position

What are the 2 types of metric georeferencing?

Geographic coordinate system and projected coordinate system

What is a geographic coordinate system?

A coordinate system directly on the Earth (includes latitude, longitude, and an angle to define position)

What is a projected coordinate system?

A coodinate system on a flat surface (uses x, y coords to define position)