Presentation on theme: "Geographic Base Maps; Map Projections; Using MapInfo Help I.Geographic Base Maps A.Definition B.Types 1. TIGER/ Line 2. Cadastral 3. Planimetric II. Map."— Presentation transcript:
Geographic Base Maps; Map Projections; Using MapInfo Help I.Geographic Base Maps A.Definition B.Types 1. TIGER/ Line 2. Cadastral 3. Planimetric II. Map Projections A.Definition B.Types III. MapInfo Help A.Using Index Option B.Using Search Option
Real world is complex – How do we represent features in GIS? Features are shown as spatial objects: points, lines, or polygons
Geographic Base Map: The computerized data layer(s) that contain all geographic (spatial) objects that are common to user(s). The geographic base map is the first layer(s) placed on the GIS display. Other data layers are then placed above and used for analysis in project work. The needs, uses, or application of the user determines the types of map layers and detail required.
THE 3 MOST COMMON BASE MAP FILES 1.TIGER Line 2.CADASTRAL 3.PLANIMETRIC
First major Base map Type: TIGER/ Line files - Electronic map files (layers) that display various map features - Developed by U.S. Census Bureau to aid in the census (counting population) - Topological Integrated Geographically Encoding & Referencing - Covers the entire United States
USGS Topographical Map TIGER spatial objects captured from USGS 7.5 min. quadrangles Quads were about 50 sq. mi. (7x7miles) Scale 1:24,000 (1 inch = 2,000 feet) Features are displayed on the USGS quads (roads, rail, water, contours, etc.)
7.5 min USGS Quad Index for NE Ohio 57,000 Quad Maps in US Features digitized & spatial objects created in TIGER 7.5 min quad
Example Data Layers (spatial objects) in TIGER 2010
Demographic data captured in the Census can be linked to each block & displayed or analyzed. This attribute data is available through the US Census Bureau. dBase files or excel spreadsheets can be created from the attribute data.
Example of TIGER File –Record Type 1 Until about 1995, the files were available - at a cost - on tape (not CD) - had to use a programming language like SAS to translate to the GIS software desired.
TIGER files can be acquired for any county in the US: Free from various websites: http://geodata.gov or http://www.census.gov/geo/www/tiger/tgrshp2010/tgrshp2010.html Files are provided in ESRI shapefile format. Files can be translated to MapInfo format or opened directly to MapInfo.
Second Major Base map Type: Cadastral - official record describing/ recognizing the legally defined registration of land (property) - often referred to as the “parcel base map” - created by County Auditor or Tax Assessor - used for tax assessment, public services, zoning, etc. Based on Legal definitions of parcels (property) ie. From a surveyed x,y location, move North 62 degrees East for 157 feet, move South 91 degrees West, move … until reaching the original x,y location thus creating a parcel polygon (area)
Cadastral Base Map Example Paper Maps are contained in 292 Books in Cuyahoga Co. About 30 map pages per book 8814 individual paper map pages Paper maps digitized Information is historical Digitized as lines NOT polygons
Parcel polygons created paid for: by Cleveland Water Dept. Currency: Complete through Nov. 1994 County updates parcel file all year long. County Auditor’s Office has been updating parcels to the present. NODIS receives periodic updates to the parcel layer. Auditor also maintains attribute databases containing information about each parcel
Third major Base map Type: Planimetric - Physical features that can be seen on ground are spatially recorded (mapped) - Examples of features captured are road edges (curbs), building footprints, railroads, 2 & 10 foot elevation contours, spot (point) elevations, retention walls, driveways, bridges, interstates, recreation areas, and trees. - Cuyahoga Co. Engineer’s Office – funded the process to create the planimetric layers - Planimetrics are created from aerial photography
Orthogonal Rectification: - process to correct the aerial photo distortions - uses mathematical algorithms to correct - a very technical, detailed, & complex process After aerials are rectified: - orthophotos are generated with corrected shape, elevation, and spatial location of the features captured - There are 1110 orthophotos for Cuyahoga Co. - orthophotos are spatially located, placed side by side similar to putting a puzzle together Planimetric data layers are then electronically captured and placed into the correct data layer. Ie. Road edge, building footprint, etc.
Shows the 1,110 individual orthophotos Flown in 1993, created orthophotos and planimetrics Flown again in 1999- not processed to planimetrics Flown again in 2002- not processed to planimetrics Flown again in 2006, created orthophotos & selected planimetrics (1/2 foot accuracy) Flown again in 2008- not processed to planimetrics
Planimetric - NODIS joined all 1110 planimetric files into a seamless layer for the county. ie. There is ONE data layer for building footprints not 1110 individual building files. This was done for the other planimetric layers. - positional accuracy of planimetrics layers are high (plus or minus a few inches to a few feet)
What Base Map do I use??? - depends on user application or project The base map used can be: - 1 or more data layers within one base map type - or a combination of data layers from more than one base map type
Map Projections: - The process of converting 3 dimensional features to 2 dimensional objects. - Over 50 major map projections with many subtypes - 2 major projection types deal with: Equal Area Direction
Map Projection Examples Equal Area Projections attempt to display features with lowest amount of area distortion Direction Projections Attempt to display features For navigational purposes (To get from point A to B) Direction Projection
Latitude- Longitude - is NOT a projection - actual measured angles from the center of the earth - grids are equal size - stretches US, Anactica, etc. U.S. State Plane- Northern Ohio NAD83 - best use is local maps in Northern Ohio - units are in feet
Any projection type is acceptable to use when project work is in a small geographic area. Large scale maps = small geographic area ie. 1 inch = 50 feet Small scale maps = large geographic area ie. 1 inch = 50 miles
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