GIS Applied: Two Big Questions Where is what? Obtain information from a location What is where? Query information to find location

Methods of representing geographic space Geometric data models Vector Raster

Geometry, topology and attributes Geometry: coordinates and form of the objects Topology: adjacency relations of objects Attributes: properties, values Example: Country map of South America Geometry: coordinates of the borders Topology: the countries border Attributes: names of countries, population, etc.

Organized collection of: 1.4. GIS Components Organized collection of: Hardware Network Software Data People Procedures People Software Data Procedures Hardware Network

Scanner © 2005 John Wiley & Sons, Ltd

Digitizers

Digitizer © 2005 John Wiley & Sons, Ltd

Typology of human errors in digitizing: (A) undershoots and overshoots; (B) invalid polygons; and (C) sliver polygons

Error induced by data cleaning

Mismatches of adjacent spatial data sources that require rubber-sheeting © 2005 John Wiley & Sons, Ltd

1.5. How To Use GIS (GIS Applications) 1) Mapping Where Things Are Mapping where things are lets you find places that have the features you are looking for and to see where to take action. Find a feature—People use maps to see where or what an individual feature is. Finding patterns—By looking at the distribution of features on the map instead of just an individual feature, you can see patterns emerge. 2) Mapping Quantities People map quantities, such as where the most and least are, to find places that meet their criteria and take action, or to see the relationships between places. This gives an additional level of information beyond simply mapping the locations of features.

3) Mapping Densities While you can see concentrations by simply mapping the locations of features, in areas with many features it may be difficult to see which areas have a higher concentration than others. A density map lets you measure the number of features using a uniform unit, such as acres or square miles, so you can clearly see the distribution. Mapping density is especially useful when mapping areas, such as census tracts or counties, that vary greatly in size. on maps showing the number of people per census tract, the larger tracts might have more people than smaller ones. But some smaller tracts might have more people per square mile—a higher density.

4) Finding What's Inside Use GIS to monitor what is happening and to take specific action by mapping what is inside a specific area. For example, a district attorney would monitor drug-related arrests to find out if an arrest is within 1,000 feet of a school—if so, stiffer penalties apply 5) Mapping Change Map the change in an area to anticipate future conditions, decide on a course of action, or to evaluate the results of an action or policy. By mapping where and how things move over a period of time, you can gain insight into how they behave. For example, a meteorologist might study the paths of hurricanes to predict where and when they might occur in the future. 2) Map change to anticipate future needs. For example, a police chief might study how crime patterns change from month to month to help decide where officers should be assigned. 3) Map conditions before and after an action or event to see the impact. A retail analyst might map the change in store sales before and after a regional ad campaign to see where the advertisements were most effective.

LOCATION: What is at...? Here we are seeking to find out what exists at a particular location. A location can be described in many different ways using, for example, place name, or latitude and longitude coordinates

LOCATION: What is at...? Identifier: 565-88-221 Area: 108,900,245 Owner: John Morris Address: 3233 Texas St. Zoned land use: Industrial Assessment: $950,000

LOCATION: What is at...? Getting other types of information about a feature

CONDITION: Where is it? Instead of identifying what exists at a given location, you want to find a location where certain conditions are satisfied. For example, you wish to find a house assessed at less than $200,000 with 4 bedrooms and made of wood.

CONDITION: Where is it? Find features based on attributes they share Map Result 4 Bedrooms Within a certain price More than a certain area

TRENDS: What has changed since...? This seeks to discover the differences between an area as the result of the passing of time.

TRENDS: What has changed since...? City in 1950 City in 1990

What spatial patterns exist? This seeks to discover what types of patterns may exist in the newly created data file that were not visible before. For example you may wish to know where motor vehicle accidents occur and at what times.

What spatial patterns exist? What kinds of patterns exist for motor vehicle accidents? Where do they occur and at what times?

What spatial link exist? Spatial Query: What spatial link exist? GIS locates features with regards to their location to each other: Features adjacent to… Features within a certain distance Features within a certain area Etc…