ABT 150 Study Guide

What are the seven possible states of geospatial data in regards to projection and projection definition?

1. projected (ex= albers, UTM) & Defined,correctly. 2. Projected& Defined, incorrectly 3.Pojected & undefined. missing .prj file 4. Not projected (ex=GeoDD) & Defined, correctly 5. Not-projected & defined. Incorrectly 6.not-projected &undefined missing .prj file 7. Not projected & undefined (ex=scan of paper map or image file of map like .prj)

Name the three types of vector data. Describe which data type would best represent the following: a) the location of bus stops b) creeks c) soil type. why?

1.Points :bus stop 2. Lines: Creeks 3. polygons: Soil type

which raster function is used to calculate slope? How is slope calculated using a (raster) DEM? What are the two options for units of calculating slope in ArcGIS?

2 Unit options for slope: degrees or precent raster function for slope:

What is a 7.5 minute USGS quadrangle map? How does the USGS define them? What is the RF scale? How many feet does one inch on a quadrangle map represent?

A 7.5 min quadrangle map is one of the smaller quadrangles within the map products defined by the graticular network of lat/long. 60 minutes is equal to one degree (lat/long), therefore 7.5 min is .125 degree. The RF scale is 1:24,000 (1m:24,000m) one inch on a quadrangle map represents 2000ft.

What is a digital orthophoto quarter-quadrangle (DOQQ)? How many minutes does a DOQQ cover?

A DOQQ is divided into 4 quadrants minutes:3.75

Coverage

A data model for storing geographic features. a coverage stores a set of thematically associated data considered to be a unit typically representing a single layer(e.g. soils, streams, roads, or land) In a coverage features are stored as both primary a secondary features. Feature attributes are described & stored in feature attribute table

What is the geodetic datum? Contrast an earth centered datum and a local datum. Give examples of each.

A datum that is the basis for calculating positions on the earths surface or heights above or below the earths surface. Earth Centered- horizontal geodetic datum based on a ellipsoid that has its origins at the earths centered mass (NAD 83) they are more compatible with GPS than local datums. Local- horizontal geodetic datum serves as a basis for measurements over a limited area of the earth. Origin at a location on Earths Surface that uses an ellipsoid whose dimensions conform well to its regions of use originally defined for land based surveys ex NAD 27 All vertical Datums are local NAD 83 is local in a sense they are applied to a particular part of the world.

Hillshade

A graphic method that simulates how the land surface looks with the interaction between sunlight and landform features (shaded relief). Brightness of illumination of a surface from a specified light source.

geoid

A hypothetical surface representing the form the earth's oceans would take if there were no land and the water were free to respond to the earths gravitational centrifugal forces, the resulting geoid is irregular and caries from a perfect shape by as much as 80 m above and 16m below its surface

Secant Projection

A project whose surface intersects the surface of the globe ( at lines of intersection also free from distortion) ex: secant conic/cylindrical projection is recessed into globe, intersecting at two circles.

What information is in a projection file? What are the common spheroids and datums used for map projections?

A projection has the following information: projection. units, parameters, datum, spheroid. Spheroids: [types: sphere, oblate spheroid (ellipsoid) geoid] Common datums and spheroids: WGS84 (GRS80 Spheroid), NAD83 (GRS80 Spheroid), NAD27(Clarke 1866 spheroid)

Coordinate system

A reference framework consisting of a set of points, lines, and or surfaces, and a set of rules, used to define the positions of points in space in either 2 or 3 dimensions. (e.g. Cartesain VS Geographic

What is the Geographic Coordinate system (GCS)? What is GRS80? What are the units of a geographical coordinate system? (Hint: where are geographic coordinates measured from?)

A reference system that uses lat/long to define the locations of points on the surface of a sphere or spheroid. Includes datum, prime meridian and angular unit GRS80-Geodetic reference system of 1980, the standard measurements of the earths shape and size adopted by the inter nation union of geodesy and geophysics in 1979

Data Model

A standardized data base schema; a set of database design specifications; all tables & fields have the same names & definitions for all instances of all data model; allows construction of large, customizable databases (e.g. multiple counties for soil database); 4 general types: binary, index, regression, & process

what are the variables in a projection file? What is a word file? in lab 1 what was a .aux file associated with?

A word file is a plan text computer data file used by GIS to georeference raster map images/contains info about where an image should be displayed in real world coordinates. Coordinate system, spatial domain (xy values), Coordinate Precision .aux is used for handling a raster dataset stored in the file system.

Thematic Layers

AKA Data theme; A collection of common geographic elements such as road networks, collection of parcel boundaries, soil types, elevation surface, satellite imagery etc. Specific to a certain location/area; each layer contains spatial information for only one theme (one layer for soil features, one layer for elevation, etc) but can come together to reveal spatial relationships; thematic layer VS general reference.

integar Raster

AKA Discrete Raster; represents data that has clear boundaries (whole numbers_ with attributes that are descriptions, classes, or categories. Integers are used to represent cell values and each value must fill the entire cell. (ex. With regional planning, value 1 will represent agricultural land, value 2 will represent urban land, value 3 will represent green space, etc)

Latitude

AKA parallels; angular distance measured in degrees north or south of the equator; lines that run east to west

Of those discussed in lecture, which map projection is best for a statewide map of CA

Albers Equal Area Conic

Primary Key

An attribute or set of attributes in a database that uniquely identifies each record. Primary key allows no duplicate values and cannot be null. Used with foreign key to join tables in a database

Longitude

Angular distance usually expressed in degrees, mins, and sec, of the location of a point on the earths surface east or west of the arbitrary defined meridian (typically Greenwich prime meridian) all lines of longitude are great circles that intersect the equator and pass through the North and South poles.

What are the names of the three main component (software) programs in ArcGIS? Describe the principle function of each platforms.

ArcMap: Geovisualization ArcCatalog: Geoprocessing ArcToolbox: Geodatabase

In color theory, what are the two color models used to: 1.) Display color on computer screens and 2.)printing?

CMYK -printing RGB- Display images on a monitor

What is CalAtlas? What kinds of data are available?

CalAtlas is a geospatial clearinghouse for the state of CA and contains its geospatial data and maps.

Summary Table

Calculates statistics for groups of features in table; groups by unique values in the one field; user chooses statistics to calculate for other fields; produces additional table with groups and stats,

What are the fundamental concepts of topology?

Connectivity (a start and end node join to make an arc) Containment (closed connected arcs surrounding an area) Adjacency (polygons on each side of an arc)

What is a dilution of precision (DOP)

Create polygons from polylines (feature conversation tool in ArcToolbox) attribute the polygons in the database check the database for errors

List at least three types of common topological errors.

Dangle, Overshoot, Overlap, and nonsensical vertex order

Feature Attribute Table

Databases or tabular file containing information about a set of geographic features usually arranged so that each row represents and feature & each column represents a feature attribute.

Aspect

Direction of steepest slope. Which was the slope faces 0-360

Describe and sketch the 'clip' vector overlay function and the 'dissolve' function. How does dissolve work to generalize a map?

Dissolve: process of removing unnecessary boundaries between features such as Edges or adjacent map sheets after data has been captured. Clip: themes like a cookie cutter on your input theme, input theme attributes are not altered (polygons, lines, points)

Describe the minimum mapping unit (MMU) concept? Why do we need to specify it?

For a given scale, the size in the map units below which narrow feature can be reasonably represented by a line and an area by a point.

Describe the main steps to create a polygon feature class

Georeference a scan or photo digitize polylines match edges rubber sheeting (align one layer with another) Topological validation (detects errors in digitizing)

What is the State plane coordinate system? Which map projections are used and why?

Group of planar coordinate systems based on the divisions of the US into more than 130 zones to minimize distortions caused by map projections. Each zone has its own map projection and parameters and uses either the NAD27 or NAD83 horizontal datum. The lamber conformal conic projection is used for states that extend mostly east-west while tranverse mercator is used for those that extend most North-south. The oblique mercator projection is use for the panhandle of Alaska.

What measurement units are used for cell values in rasters of hill shade (shaded relief), slope, and aspect?

Hillshade: Bightness/illumination from a specific light source in grayscale values Slope: Rate of elevation change in degree or percent Aspect: Direction of steepest slope in degrees

What are hue, value, chroma? Describe the difference between complementary and analogous color on a standard color wheel. When would you use complementary (vs analogous) colors to symbolize a map?

Hue: The actual color (yellow, red, blue etc) Value: The lightness or darkness (greyscale) chroma: intensity of the color Analogous colors are colors next to each other on the color wheel and transition into each other while Complementary colors are on the opposite sides of the color wheel and contrast heavily. You would use analogous colors on a map when demonstrating different elevation levels or anything in the same category (elevation, depth, shadows etc) in order to show a smooth transition. You would use complementary colors for different items on a legend (roads vs lakes, highway vs, soil types) so that they are easier to tell apart.

Explain the difference between hydologic regions and hydrologic units in the hierarchal naming system of watersheds used by the CALWATER database.

Hydrological units (ie: rivers, lakes, etc) are nested within hydrological regions. (i.e.: Sac watershed), which constitute the least specific level of watershed classification Region=Watershed or sub-watershed Unit is within watershed as a lake, pond, river, etc.

What is the difference between a single-part VS a multi-part feature? What function would you use to create a multi-part feature?

In the attribute table A single part feature - each row or record corresponds to a specific feature A multi part feature- each row or record can correspond to a group of feature lines or polygons, use ArcToolbox to create multipart feature out of many single part features.

What is the concept of differential GPS? Where can the differential correction be obtained from?

Increased accuracy, uses one stationary and one mobile receiver to overcome errors. Stationary receiver must be on a known control point, with known value, in order to calculate error, which it then sends to the mobile receiver.

What effect does it have on measurement accuracy?

Indicator of satellite geometry that accounts for the location of each satellite in relation to others. When satellites are close together the accuracy is lower and the DOP is higher. Optimal accuracy is when satellites are far apart and the DOP is low.

Define GIS. Identify and describe two main components that make up a generic GIS. Name at least 3 different types of products that can be generated using a GIS.

Integrated collection of computer software and data used to view and manage information about geographic places, analyze spatial relationships and model spatial processes. Proved framework for gathering and organizing spatial data and related information so it can be displayed and analyzed . Products: 1. Models 2. Maps 3. Databases

What is unique about RTK GPS

It provides accuracy within centimeters

Name the three ways to display layers in the TOC of ArcMap

List by Source, List by drawing order, list by selection

If a data layer (ex: feature class, raster, or image) is unprojected, can it have a projection file?

No the data layer is undefined unless a projection file is present. Otherwise it is just in geographic coordinate system until defined with the projection file.

If a data layer (feature class, raster, or image) is missing a projection file, is the data layer 'defined'?

No, it is not. If any part of the projection definition of new data added does not match the data frame's projection parameters then it may not spatially align.

NAD 27

North American Datum of 1927, based on the clarke 1866 spheroid, local datum, from land-based surveys, origin in Kansas. Invented space travel, shift from optical surveys to a mathematical model of the earths shape the result is that a specific point on the landscape can take on multiple meanings.

NAD 83

North American Datum of 1983, based on the GRS80 spheroid, global datum, satellite based system, geocentric.

If the representative fraction (map scale) printed on a paper map is shown to be 1:100,000 what does one inch represent? And for 1:62,500? How many feet does one inch represent in each case?

One inch of map distance corresponds to 100,000 inches of distance on the earths surface, or one foot on the map represents 100,000 ft on the ground. Likewise, one inch corresponds to 62,500 inches on the earths surface and 62,500 feet on the ground.

Describe the Public Land Survey System (PLSS) and why it is used. Describe the township and range coordinate system. What is a township and a section? How much area is covered by a section? What is cadastral mapping?

PLSS is the US survey method used to divide land property for sale and settling, designed in 1785 to survey land ceded to the US by the Treaty of Paris (1783). USed throughout most of the country, the land is divided into Township lines and Range lines. A Township is nominally six by six square miles, and consists of 36 sections, each square mile. Cadastral mapping is a comprehensive map of the real estate and ownership of an area.

Describe two types of data structures for representing vector data, and what are the pros and cons for each?

Points (discrete), lines, polygons, TINs- (pros and cons?) Vector advantages: Compact data structure, very small features can be shown. Vector disadvantages: More complex structure,data capture can be slow, overlay operations are difficult to implement.

For spatial data projection distinguish between 'project' and 'define projection' tools in ArcToolbox

Project > Drag a file in, convert from one coordinate system to another Define Projection > When a coordinate system is not already in place or modifying the one already in place; in ArcToolbox define projection creates a txt file that outlines the spatial reference. defining constraints, i.e. spatial reference.

.prj

Projection file

Distinguish raster from vector data. What are the main differences? Contrast continuous phenomena mapping (ex topography) from discrete (categorical data). Which one is best represented by raster data and which one is best represented by vector data?

Raster: Representation of the world as a cur face divided into a regular grid of cells, useful for storing data that varies continuously (ariel photo, satellite image, elevation surface) raster coordinates are contained in the ordering of the matrix Vector:Stores coordinates explicitly. represents geographic features as points/lines/polygons. attributes are associated with each vector feature useful for storing data with discrete boundaries (country borders, land parcels, streets).

Slope

Rate of change of elevation. Calculation based on surrounding cells

Datum

Reference specifications of a measurement system, usually a system of coordinate positions on a surface (horizontal datum) and a system of coordinate positions above and below the surface (vertical) Datum is build upon the spheroid.

Distinguish between an absolute path and a relative path in ArcMap

Relative path- location of a computer file given in relation to the current working directory. Absolute Path- (or full paths) path identifies a unique location in a file system following the directory tree hierarchy.

What is SSURGO Data? Which agency creates and distributes these data?

SSURGO data contains information about soils as collected by the National Cooperative Soil Survey over the course of a century. The US department of Agriculture (USDA) creates and distributes the data.

What is the difference of area (or perimeter) attribute shown in the geodatabase polygon feature classes and shape files?

Shapefile does not automatically contain geometry feature class contains geometry feature.

.shp

Shapefiles

Describe each of the six database field types in ArcGIS. What is a "float"field type? What is precision and scale?

Short integer- numeric values without fractional values, small range Long integer- numeric values without fractional values, large range Single precision floating point number- numeric values with fractional values, smaller range double precision floating point numbers- numeric values with fractional values, large range. text-up to 64,000 characters date-time and date BLOP-Images or other multimedia Precision- a measure of the control over random error, those closeness of a repeated set of observations of he same quantity to another the number of significant digits used to store numbers

What are major sources of error in GPS measurements? How do we improve the accuracy of a GPS unit and measurement accuracy?

Signal errors, Atmospheric interference, multi path error (bouncing of signal), satellite position, human errors, obstruction. Improve by using open sites, during clear weather, and taking repeated measurements.

Give an example of a spatial query

Statement or logical expression that selects geographic features based on location or spatial relationship. Ex: a spatial query might find which points are contained within a polygon or set of polygons, find features within a specified distance or a feature or find features that are adjacent to each other

tangent Projection

Surface touches the globe without piercing it. A tangent planar projection touches the globe at one point, while tangent conic and cylindrical projections touch the globe along a line or lone of tangency the projection is free from distortion

Describe the process of linking database tables (joining tables). Define the origin (or source) table and the destination table. Which contains the primary key? what is a many-to-one join and a one-to-join. Draw a diagram of these processes.

Table joining expands the number of fields available to a query by appending the fields of one table to those of another. In order to create a table join, there must be a destination table and an origin table. The destination table is typically a feature class attribute table while the origin table contains the fields to be appended, the origin table contains the primary key although the destination table can also have the primary key in a one-to-one. A many-to-one join is when more than one record in the layer attribute table (destination table_ can have the same key value as a single record in the lookup table (source table). A one-to-one join is when there is one record in the layer to attribute table shares the same key value with one record in the lookup table.

TOC

Table of Contents; option in ArcMap to list layers by drawing order, by source, or by selection

What is the purpose of WAAS and what does it consist of?

The Wide Area Augmentation System (WAAS) is an air navigation aid developed by the Federal Aviation Administration (prime contractor Raytheon Company) to augment the Global Positioning system (GPS), with the goal of improving its accuracy, integrity, and availability. Essentially WAAS is intended to enable aircraft to rely on GPS for all phases of flight, including precision approaches to any airport to any airport within its coverage area.

How does "project-on-the-fly" work in ArcGIS? How can you determine the map projection of a map printed from ArcMap?

The first layer added will define the projection of the frame and the coordinate system, so that all added layers will be projected the same way. The projection should be included on the map , and is stored in the projection data file.

Which four map properties are potentially distorted by map projections? How are conformal map projections different from equal area map projections?

The four map properties it distorts is shape area distance or direction. Conformal projection preserves local shape while equal area while central meridian projects to the straight line x=0, equator projects to the straight line y=o although maintains equal area, distorts shape.

Line Weight (Map symbology)

The thickness of a line in a map. Different thicknesses convey different meaning. A thicker line or border may convey a more importance than a thin line weight.

What does a GPS system consist of? Name some operational GPS systems with global coverage and some regional GPS systems

Three segments: Control, Space, and User Global coverage: US NAVSTAR, Russian GLONASS Regional coverage: IRNSS

In cartographic map design, describe the main graphic elements of a map.

Title, north arrow, scale bar, scale text, sources, projections, legend, date, name.

What is a TIN? What data types are used to create one? Which triangulation process does ArcGIS use?

Triangulated Irregular Network- used to store and display surface models -Vector data structure that partitions geographic space into contiguous non-overlapping triangles -vertices of each triangle are sample data points with x-,y-,z- these sample points are connected by lines to form delaunay triangles. (Delaunay:circle around each triangle does not contain any other nodes) Used for topography or really any other surfaces. Reduces data redundancy. Based on vector data model because it connects between points )lines connect between points, creates triangles) Using topology to create a TIN in GIS. Points that create triangle =mass points.

How are trimmed and untrimmed DGRs different? What can trimmed DGRs be used for?

Trimmed DRGs do not have a white border around the edge of the quadrangle while untrimmed DRGs do have a white border around the edges. Trimmed DRGs can be placed next to each other to create a larger map while untrimmed cannot due to the borders. Digital Raster Graphic=DRG

What are the main components of a GPS

Two carrier frequencies, two digital codes, and a navigation message.

Which coordinate systems did we discuss in the lecture that have "zones" associated with them? What is the fundamental limitations of zones in mapping regions (ex:extensive geographic areas)?

Universal Transverse Mercator (UTM): conformal; 60 zones in the world, zone 10 and 11 in CA State Plane Coordinate System (SPC): conformal; many zones throughout the state.

What is UTM? Which projection method is used? How many zones are in CA?

Universal Transverse Mercator- a projected coordinate system that divides the whole world into 60 north and south zones 6 degrees wide. Zones in CA 10 and 11

Contour Interval

Vertical distances between contour lines

What wavelengths of light are visible to humans? Describe three behaviors of light.

Wavelengths of light visible to humans: 420-700nm Behaviors: 1.Reflected: light bounces off a surface of an object 2.Absorbed: Light is absorbed into object 3. Transmitted: Light goes through object

Spheroid

When used to reference the earth, a 3D shape obtained by rotating an ellipse about its minor axis, with dimensions that either approximate the earth as a whole or with a part that approximates the corresponding portion of the geoid.

Projection

a method by which the curved surface of the earth is portrayed on a flat surface; generally requires systematic mathematical transformation of the earths graticule of lines of long & lat onto a plane. Every map projection distorts distance, area, shape, direction or some combo thereof.

Floating Point Raster

a type of numeric field for storing numbers with a decimal point.

Shapefile

a vector data storage format for storing location, shape, and attributes of geographic features. It is stored in as set of related files and contains one feature class.

Foreign Key

attribute or set of attributes in one table that match the primary key attributes in another table. Used with primary key to join in a database

.shx

compiled version of .shp files used by AutoCAD

.dbf

dBASE database file

Schema

design or structure of a database object (e.g. tables); contains database field definition and is often stored in metadata.

Map Document

in ArcMap The file that contains one map, its layout and its associated layers, tables, charts, and reports. Map Docs can be printed for embedded in other documents uses .mxd extension

Differentiate between a layer file, shape file, feature, feature class, and feature dataset.

layer file: a file that stores the path to the source of actual data shapefile: a vector storage format for storing location, shape and attributes feature: typically a representation of a real world object (road, building etc) feature class: only exists in a geodatabase, is a collection of features with same type of geometry and attributes Feature dataset: a collection of feature classes that share a common spatial reference.

How is "resolution" defined for a raster data? What is a cell? What is a pixel?

resolution is determined by the size of cells (1m, 2m, 10m) to produce a higher definition on raster data. Smaller cell size=better resolution. The cell is what has the value for the land cover type. A pixel is a physical point on a raster image.