Introduction to Mapping Sciences: Lecture #2 (Information Representation) Information Representation...

Introduction to Mapping Sciences: Lecture #2 (Information Representation)

Information Representation

Imagery

Terrain

Thematic Maps


Imagery

Of the three types of maps discussed (image maps, physical models and line maps) image maps come closest to depicting the environment in the way we see it. Image maps are derived from systems that capture the a image of an entire region with all its "visible" details. The types of imaging systems are photographic systems, electronic sweep scanners and digital arrays.


Imagery

Photography is

The process of collecting / recording images on a sensitized surface (e.g. film) by the action of light or other radiant energy.

A Photograph is the resultant Negative or Positive


Photography Example


Imagery

Imaging is

The mapping of the intensity of radiation reaching a sensor as a function of position in a 1-D or 2-D field

Either on film, in a computer, on a CRT screen, or other display device.

An ‘image’ is the resultant map.


Imaging Example


Imagery

Photo Interpretation

The act of examining aerial photographs or images for the purpose of identifying objects & judging their significance

Photogrammetry

The science of obtaining reliable measurements by means of photography.


Imagery

Uses of Remotely Sensed Data

Background Images for GIS Overlays

Monitor Changes

Extract Infrastructure Information

Roads, Structures, etc

Disaster Effects

Extract Land Cover Information

Vegetation Cover

Water Sources


Imagery Uses


Imagery

Image vantage points are horizontal, oblique and vertical


Horizontal

This is the way we see the world. Capturing images from this vantage is problematic because of the limited area that can be seen and the variable scale associated with this vantage point.


Oblique

High oblique image are taken with the sensor inclined between 0 and 45 degrees to the horizon. The horizon is visible in a high oblique photograph. A low oblique photograph has a sensor incline between 45 and 90 degrees to the horizon. Scale for both of these images decreases from the foreground to the background.


Vertical

These are the most common type of images taken for inventory and mapping purposes. The sensor is perpendicular to the earth's surface. The greatest advantage of this type of image is that scale is relatively constant, and the block of features is minimized.


Geometric Corrections

Images have inherent distortions due to the imaging geometry of the sensor system. Photographic systems have distortions due to the perspective geometry of the photographic system and the camera orientation at the time the image is collected. These distortions have been mathematically modeled and can be corrected to produce orthophotography, a map-like image.


Terrain

Terrain is a critical aspect of our environment that limits the possible uses to which we can make of the land. Its portrayal on maps can take may forms.


Data for Terrain Mapping and Analysis

A Digital Elevation Model (DEM), consists of a sampled array of elevations for ground positions that are normally at regularly spaced intervals.


DEM Example



Triangulated Irregular Network (TIN) Series of non-overlapping triangles

Elevation values are stored at nodes

Irregular distribution

Sources: DEMs, surveyed elevation points, contour lines, and breaklines

Breaklines are line features that represent changes of the land surface such as streams, shorelines, ridges, and roads



Triangulated Irregular Network (TIN) Not every point in DEM is used Only points most important VIP (Very Important Points) algorithm Maximum z-tolerance algorithm Delaunay triangulation: all nodes are connected to their nearest neighbor to form triangles which are as equi-angular as possible.

Borders are a problem Go beyond study area and clip to make best


TIN Example


Terrain Mapping

Contouring is most common method for terrain mapping

Contour lines connect points of equal elevation (isolines)

Contour intervals represent the vertical distance between contour lines.

Arrangement of contour lines reflect topography


Contour Example


Terrain Mapping

Vertical profile shows changes in elevation along a line, such as a hiking trail, road or stream.


Terrain Mapping

Hill shading is also known as a shaded relief or simply shading

Attempts to simulate how the terrain looks with the interaction between sunlight and surface features.

Helps viewers recognize the shape of land-form features on a map.


Hillshading Example


Hillshading

Four factors control the visual effect of hill-shading

Sun’s azimuth is direction of incoming light (0 to 360°)

The sun’s altitude from horizon (0-90°)

Surface slope (0-90°)

Surface aspect (0 to 360°)


Terrain Mapping

Hypsometric tinting Applies different color symbols to represent elevation zones.


Terrain Mapping

Perspective View Perspectives are 3-D views of the terrain wherein the appearance is as viewed from an airplane. Viewing azimuth (0 to 360°) Viewing angle (0-90°) Viewing distance Z-scale is ratio between he vertical scale and the horizontal scale (exaggeration factor)

3-D draping of vector information


Thematic Maps

Planimetric maps

Attribute maps focus on the locations of specific environmental features or attributes such as highways, towns, parks and rivers .

Distribution/Statistical maps focus on the spatial variation of environmental features or themes.


Attribute Maps

Single-variable symbols: symbols that represent one kind of feature. Graphic elements used to communicate the qualitative aspects of the features are: shape, pattern arrangement, pattern orientation and color hue. (note: size, texture, color value or color intensity are reserved for quantitative representation.)


Single Symbol Variables

Point emphasis

Identifies a feature at a specific location. Qualitative feature are usually represented by pictographic or geometric point symbols.


Pictograph Example


Geometric Shape Example



Line emphasis: symbols that have obvious length and width. Form is the usual graphic element used to distinguish line features.



Area emphasis: map makers use hue, arrangement and orientation to distinguish area qualities. The use of visual elements that indicate magnitude such as intensity, texture or size are confusing when applied to qualitative data and should not be used.


Attribute Maps

Multivariate symbols: usually map makers use separate symbols for each variable. At times however multiple variables are represented. By varying symbol shape, hue, texture and arrangement map makers could show four variables at once. However, no more than two variables are usually represented.


Multiple Variables

Point emphasis:

2 variables are often represented by combining shape and hue.


Multiple Variables

Line emphasis

less useful because of the extent of the linear feature. Some examples are scenic routes and construction delays.


Multiple Variables

Area emphasis: multiple variables can be shown by overlapping regions or by combining pattern with color.


Cartograms

Area or distance are distorted to portray value


Cartogram Example


Statistical maps

Statistical maps use quantitative symbols to depict magnitude information. The graphic elements for doing this are size, pattern texture, color value and color intensity.


Statistical maps

Single Variable: to show quantitative information symbols are varied to show changes in magnitude. These symbols can be either pictographic or geometric.


Statistical maps

Point emphasis

Pictographic symbols usually vary only in size where as geometric symbols vary in texture, color value and color intensity as well as size. Creating apparent magnitude scaling of size and density compensation makes some accommodation of the limits of human perception.


Statistical maps

Line emphasis

Cartographers use proportional line symbols to show changes in magnitude. One of the most common is line thickness.


Statistical maps

Area emphasis

2-D (Choropleth)

These maps show both area and magnitude.

3-D maps

Three types of maps are the region bounded map, the perspective profile and the continuous surface shading. While effective, the exact height

at any given point is hard to determine.


Choropleth Example


Statistical maps

Multivariate symbols: showing several variables with the same symbol. Size is often used to represent multiple variables. Symbology can get complex and requires creativity.

Pie Charts

Bivariate Legends

Introduction to Mapping Sciences: Lecture #2 (Information Representation) Information Representation...

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