GIS to Go
Geographic Information Systems (GIS) answer the questions WHAT? and WHERE?
GIS allows us to store, analyze, and display information, or attributes, about spatial features. Songbirds, ships, swamps, and schools are all spatial features. That is they all have a geographic location on the earth's surface, and this geographic location can be described with mathematical coordinates. The most familiar coordinates are latitude and longitude.
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Each aerial photograph is a feature and represents a spatial footprint on the earth's surface. So the geographic location attribute of each image can be described with latitude/longitude coordinates. The coordinates are just one attribute of the image. W13 July, 2004in, etc. All of these attributes are entered into fields that make up the record for this aerial photograph. The record for this photograph has 9 fields.
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As we create records for each aerial feature, we build a database.
This database becomes the Photo tiles layer.
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| Using GIS software in conjunction with the database, we can place a dot at the location of each pair of coordinates. This shows us where that particular aerial tile is located on a map. |
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KEY CONCEPTS:
- All features have attributes and one of these attributes is a geographic location on the earth's surface described by mathematical coordinates.
- Multiple feature records are used to create databases. These databases become informational layers.
- Separate information layers are created for each feature type, e.g., aerial photographs, rivers, highways, county boundaries.
- For each information layer, geographic attributes can be represented visually on a map by dots or lines or polygons. These shape files are consistant within a layer.
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Geographic Shapes of Feature Types
KEY CONCEPTS:
- Layers can be superimposed over each other by clicking them on/off as visible layers.
- While multiple layers can be viewed at the same time, only one layer is active.
- Active means that you have access to the database for that layer. You can search the database or you can use the Identify, Hyperlink, Query, Find buttons.
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In the map below, the aerial photo layer is both visible and active. You can see the data, or attributes, associated with each tile in the layer. Other visible layers are counties, water bodies, interstates, and townships.
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