GEOGRAPHIC INFORMATION SYSTEMS Lecture 20: Adding and Creating Data

Transcription

1 Adding Existing Data Into ArcGIS - there are many different ways to get data into ArcGIS GEOGRAPHIC INFORMATION SYSTEMS Lecture 20: Adding and Creating Data Add Data - normally we use the Add Data button on the Standard Toolbar and browse to a file - we can add: - shapefiles (vector points, lines or polygons) Esri shapefile format (.shp) - feature classes from a file geodatabase Esri file geodatabase format (.gdb) - feature classes from a personal geodatabase Microsoft Access format (.mdb) - feature classes from an enterprise geodatabase e.g. Microsoft SQL format or other RDMS - continuous or discrete raster layers ARC/INFO GRID format - image layers.tiff,.img,.sid,.jpg formats - map services data layers hosted by Esri or others online - layer files A file that contains symbology and a path (eg c:\data) to the data Table Joins and Relates - once we have a shapefile or feature class added to ArcMap - we can append or access additional attribute information (tabular data) with joins and relates 1) Joins (a table join appends data from a table to the attribute table) a) one-to-one relationship - attribute information is added to features by joining data from a table with same number of records - e.g. we can join a U.S. county census table to U.S. county polygons b) many-to-one relationship - attribute information is added to multiple features by joining data from a table with fewer records - e.g. we can join data from a U.S. states table to multiple county polygons 2) Relates (a table relate provides access to tabular data related to features) c) one-to-many relationship - attribute information associated with a feature can be accessed (but not directly joined) - e.g. list of tenants living at a single address - most commonly, we bring tabular data into ArcMap in a dbase IV (.dbf) or Excel format - dbase IV is the native format for shapefile attribute tables (the.dbf part of a shapefile) Import Data - we can also import data into ArcGIS (using tools in ArcToolbox) - import implies that we have to go through a file conversion process 1) can import layers created using other GIS software - e.g. MapInfo (business GIS software) 2) can import layers created using AutoCAD - e.g. AutoCAD.dxf,.dwg formats (often with limited success) 3) can import raster image layers in either binary or ASCII formats 1

2 - in many cases the data we are interested in simply does not exist and we have to create our own data - the three most common methods of creating data are: - digitizing - heads-up digitizing of scanned maps or digital imagery - digital image processing - requires the use of remote sensing software - mobile field mapping - most commonly involves the use of GPS 1) Digitizing - most GIS data are created by digitizing either scanned paper maps or digital remote sensing imagery - in older times, paper maps were digitized directly on a digitizing table using a digitizing puck - today, we use heads-up digitizing - the process of tracing features on the computer screen using the mouse - to digitize features, the process is fairly straight forward: - open ArcCatalog and create a new empty shapefile or feature class in a geodatabase - the new shapefile or feature class can be a point, line or polygon layer - the layer must be assigned a coordinate system (either geographic or projected) - the assigned coordinate system must match the coordinate system of the image layer - open ArcMap and add the image layer (either a georeferenced scanned map or digital imagery) - add the new empty shapefile or feature class to the Table of Contents - use the Editor toolbar and Start Editing to begin an edit session - select a template and a tool and use mouse clicks to trace the feature of interest - double click to finish - the new feature is created then select Save Edits (good practice) - we can now add attribute information to the records in the attribute table - repeat the process for each feature - finally, select Stop Editing and Save Edits 2) Digital Image Processing - digital image processing requires the use of specialized remote sensing software - example software includes: ERDAS Imagine, ER Mapper, ENVI - the image processing software is used to classify the features in a digital satellite or airborne image - the software classifies the features based upon a unique image signature (multiband reflectance) - imagery can be classified to map land use, vegetation, crop types, water bodies, urban areas, etc - two examples of data layers derived from image processing include: - the National Land Cover Dataset (NLCD - available from the USGS) - the National Cropland Data Layer (available from the NRCS) 3) Field Mapping with GPS (Global Positioning System) - today, GPS is the most widely used method of field data collection - we can add GPS data (lat, long) to ArcMap using Add X,Y data from the File > Add Data pulldown menu - if we Add X,Y data, the points are drawn directly from a table (e.g. Excel) and displayed as a Event layer - an Event layer looks like a point feature class in ArcMap, but points are displayed directly from the table - to use the x,y data, we must export the Event layer to either a shapefile or feature class - note: some GPS software can also save field data (points, lines, polygons) in an Esri format - in this case, we can simply add the shapefile or feature class from the GPS output 2

3 GIST 3300 / GEOG 5300 Adding Existing Data and Adding data into ArcGIS - Add data - Join and relate tabular information - Import spatial and tabular data Creating your own data - Digitizing - Digital image processing - Mobile field mapping with GPS Getting Data Into ArcGIS Add Data - normally we use the Add Data button on the Standard toolbar - we can add: - shapefiles (.shp) (vector points, lines and polygons) - feature classes from a file geodatabase (.gdb) - feature classes from a personal geodatabase (.mdb) - feature classes from an enterprise geodatabase e.g. Microsoft SQL format or other RDMS - raster layers (either continuous or discrete) ARC/INFO GRID format - image layers (airborne or satellite imagery).tiff,.img,.sid,.jpg - map services data hosted by Esri or others online - layer files (symbology and a path to the data) 1

4 Getting Data Into ArcGIS Joins and Relates - once we have a shapefile or feature class added to ArcGIS - we can append additional attribute information with a table join 1) Joins - works if we have: - one-to-one relationship - attribute information is added to features by joining data from a table with the same number of records - e.g. we can directly join a U.S. county census table to U.S. county polygons - many-to-one relationship - attribute information is added to multiple features by joining data from a table with fewer records - e.g. we can join data from a U.S. states table to multiple county polygons in a U.S. county layer Getting Data Into ArcGIS Joins and Relates - once we have shapefile or feature classes added to ArcGIS - we can access additional attribute information using a table relate 2) Relates - works if we have: - one-to-many relationship - attribute information associated with features can be accessed (but not directly joined) - e.g. list of tenants living at a single address, or one parcel has many owners Tabular Data Formats - most commonly we join or relate tabular data in a dbaseiv (.dbf) or Excel format 2

5 Getting Data Into ArcGIS Import Data - we can also import data into ArcGIS (using tools in ArcToolbox) - import implies that we have to go through a file conversion process - we can import: 1) layers created using other GIS software - for example MapInfo (business GIS software) 2) layers created using AutoCAD: - for example.dxf or.dwg files - often with limited success 3) raster layers in either binary or ASCII formats Three most common methods of creating GIS data: 1) Digitizing - heads-up digitizing 2) Digital image processing - involves the use of remote sensing software 3) Mobile field mapping - Global Positioning System (GPS) 3

6 1) Digitizing - involves tracing features from an existing source - usually hardcopy air photos or a hardcopy map Digitizing Table dated hardware 1) Digitizing (heads-up digitizing) - today, paper maps are scanned with a large format scanner to create a digital map image - the digital map image is then georeferenced - features are created by digitizing on a computer screen 4

7 1) Digitizing (heads-up digitizing) - in Catalog or ArcCatalog create a new, empty feature class in a geodatabase - the new feature class can be a point, line or polygon layer - the layer must be assigned a coordinate system (geographic or projected) - the coordinate system must match the image layer that is being digitized - open ArcMap and add the image layer (scanned map or digital imagery) - add the new feature class to the Table of Contents - use the Editor toolbar and Start Editing - select a template and a tool and use mouse clicks to trace the features - once a new feature is created then Save Edits - add attribute information to the records in the attribute table - repeat the process for each feature - finally, select Stop Editing and Save Edits 2) Remote Sensing and Digital Image Processing - image processing software can be used to classify imagery - the classified image is a raster dataset that can be added to ArcMap - most often, imagery is classified in order to map land use - e.g. National Land Cover Dataset (NLCD) - e.g. National Cropland Data Layer - or land use change 5

8 3) Mobile Field Mapping with GPS - today, GPS is the most widely used method of field data collection - we can add GPS data directly into ArcMap using Add X, Y Data from the File > Add Data pulldown menu - then convert the Event layer to a shapefile or feature class 6