Laserfiche WebLink
<br /> <br /> <br />.'_.... n.,. <br /> <br /> <br />However, when you zoom-in and examine them more closely, <br />you will notice that the 1:100,000 data (dotted lines) has much <br />less detail. The stream segments are straighter; smaller streams <br />are often omitted, The trade off between using large scale <br />(detailed) data and small scale (less detailed) data usually <br />involves issues such as storage space (the layer created from <br />1:24,000 scale map is approximately 0,5 MB (500 KB) in size, <br />while the layer created from the I: 1 00,000 scale map is only 31 <br />KB in size), availability, cost of production and draw time. <br /> <br />If the data are intended to be used as part of a dataset displaying an extensive area, it is probably not efficient <br />to use data derived from detailed scale maps. Scale can also be important when displaying data from <br />different sources at the same time, Two layers derived from the same scale maps match much better than the <br />data derived from maps of different scales, <br /> <br />Part 6: Types of spatial data available <br /> <br />Spatial data are available from government agencies or commercial firms, These data are in many different <br />formats. Some common vector data formats include the US Census Bureau data in TIGER files, AutoCAD <br />DXF mes, topological maps such as USGS DLG data, MapInfo MlF mes, MapInfo table mes, ARCIlNFO <br />coverages, ARCIlNFO Export mes, and ArcView shape meso Raster me formats include ARCIlNFO Grid <br />mes, ERDAS Imagine mes, ERDAS LAN or ERDAS GIS, BIL, BSQ, and BIP to name a few. <br /> <br />Most GIS software have their own native format. Many can also read data in other formats as discussed in <br />the next section. <br /> <br />The data used in the Digital Hazard Data class were derived from a variety offormats and sources, The data <br />dictionary in your course materials lists the source of the data. Some data are in ASCII text format and can <br />be viewed with word processing software. A word processor cannot display the data in graphic format but <br />will allow you to see what the me contains. The FEMA DFIRM flood data, which you will use in the class, <br />is available in USGS DLG format. USGS DLG and other ASCII data formats can be viewed with a word <br />processor. <br /> <br />70f9 <br /> <br />3/17/9810:05 AM <br />