Presentation on theme: "Center for Modeling & Simulation. A Map is the most effective shorthand to show locations of objects with attributes, which can be physical or cultural."— Presentation transcript:
A Map is the most effective shorthand to show locations of objects with attributes, which can be physical or cultural in nature It is an abstraction process by which real-world objects are measured, documented, and stored on a medium which generally is a paper It is therefore simplified and reduced in size It is a graphical / dynamic representation of geographic data Spatial data stored in the maps can be described by three concepts Entity Attribute relationship
Entity: it is a distinct spatial object of interest e.g. river, road etc Attribute: a description of some aspects of the entity e.g. name, length, width, volume of flow etc Relationship: spatial association among the entities etc river draining into the lake or sea
Share knowledge about world in many ways Identify a location and its attributes Locate where you are With the aid of GPS you can also monitor speed of travel and direction Identify distributions, relationships, and trends which are not otherwise discernible Integrate data from diverse sources into a common geographic reference Combine and overlay data to solve spatial problems
Can find best path between one point and the other Model future events
If both describe the spatial data by concept of entity, attribute and relationship then Why is GIS better then maps?
MapsGIS Unstructured representation entity generally represented by symbols as attributes Structured data according to entity type along with the table of attributes (database) Relationships on the maps is depicted visually They are stored either explicitly as topology
General purpose/Reference Maps: Not designed for any specific application Focuses on locations Show variety of physical and cultural features Good base-maps for determining distance, areas, directions and cordinates In GIS used for locational information of the spatial data E.g. toposheets
Special purpose/Thematic Maps Designed to depict a particular type of feature or measurement only Produced at different scales using the reference maps In GIS depict geographical phenomenon and processes E.g. maps of population distribution, landforms, rainfall, rivers etc.
Geographic features can be natural or manmade Three ways of presenting the geographic features on the map are Discrete features Image or sample grid surface
Have distinct shapes represented by points, lines and polygons Points: features too small to represented by lines or areas Lines: features too narrow to be represented by area Polygons: closed figures representing the shape and location of the homogeneous features
They are raster formats It is a two-dimensional matrix of cells Represent qualities such as colour, spectral reflectance, rainfall
Some aspects of the earth’s surface can be drawn as features like ridges, peaks, streams etc Surface display portrays the shape of the earth, like elevation, slope etc Similarly population density can also define the surface
Features on the maps are present within the database table and can be accessed through links to other databases There can be numerous attributes to a feature The most common are
Descriptive string: giving name, condition, type or category Coded Value: Giving type of feature (numeric or abbreviated string) Discrete numeric value: resents something that can be counted like, lanes on roads Real numeric value: represents continuous data that can be measured or calculated like distance, area or flow Primary key: A key to access attributes in the external database
Depicting type attributes: Coded values are used to draw symbols which depict the type of object Illustrating measured attributes: numeric values can be drawn on the map by varying size of the symbols Classified attributes: coded or numeric values can be resented by colours, which represent features which share a common value Descriptive attributes: Descriptive strings can be drawn, next to, along or inside the features
Maps visually reveal Which features connect to others Which features are adjacent to others Which features are contained within an area Which features intersect Which features are near others Difference in elevation of features Relative position among features Maps in GIS also support spatial queries that list and select
◦ Title ◦ Direction ◦ Scale ◦ Legend ◦ Features http://geodepot.statcan.ca/Diss/Reference/Tutorial/RM_tut2_e.cfm
Mapmakers usually orient their maps to show north at the top.
How distance on the map relates to distance on the ground. Any scale can be used for a map, but a few common scales have been settled on for use by most organizations, like 1:24,000 by USGS 1:63,360 - 1 inch equals 1 mile 1:50,000 1:250,000 1:1,000,000
Scale is expressed in 3 ways. 1.In words (One cm = One km) 2.Representative fraction (RF as 1:63,360, 1:25000 ) TRICK - REMOVE LAST 2 ZEROS TO GET ACTUAL SIZE ON GROUND IN METRES 3.Linear scale – Bar scale
Smaller the number on the bottom of the map scale, the more detailed the map will be and is called as large scale maps. Larger number on the bottom of the map shows fewer details and is called as small scale map A 1:10,000 map will show objects ten times as large as a 1:100,000 map but will only show 1/10th the land area on the same sized piece of paper.
Large scale maps have a scale of 1:50,000 or greater (1:24,000, 1:10,000,...). Maps with scales from 1:50,000 to 1:250,000 are considered intermediate. Small scale maps are those with scales smaller than 1:250,000. Here are 3 views
The legend is the key to unlocking the secrets of the map.
Typical RFLarge ScaleMedium ScaleSmall Scale Depicts small features Small feature disappear Symbolise features eg. Areas represented by points CharactersShow geometric shapes Generalise geometric shapes Show macro features like climate zones Good compromise between map details and extent of map coverage