07/05/2013

The difference between joining layers by merge and union





Perbezaan antara menyambung lapisan mengikut  merge dan union

Lihat baik-baik sebelum anda keliru. Tahulah terdapatnya dua cara untuk menyambung lapisan: melalui merge atau union dimana kedua-dua merupakan modul Vecktor. Yang pertama terletak pada Data Management Tools/Merge Shapefiles To One manakala yang kedua terletak pada Geoprocessing Tools/Union.  Di kes pertama, attribute tables dari lapisan berbeza bersambung tapi tak berintegrasi. Di kes kedua, attribute tables dari lapisan berbeza berintegrasi terus membolehkan pertanyaan SQL. Oleh itu, gunakan Union jika hasratnya adalah untuk menjalankan SQL query yang melibatkan attribute tables dari dua lapisan. Saya masih belum tahu bilakah untuk menggunakan alternatif Merge Shapefiles To One ...kepala saya masih malas nak fikir lanjutan PRU, rasa macam cuti awam.

The difference between joining layers by merge and union

Look closely before you get yourself confused. Know that there can be two ways to join layers: by merging or unionizing them both of which are possible via Vector modules. The former uses Data Management Tools/Merge Shapefiles To One whereas the latter uses Geoprocessing Tools/Union. In the first example, attribute tables from different layers simply join each other but do not really 'merge' in the sense of the word. In the second example, attribute tables from different layers properly merge making it possible to do SQL query. Thus, use Union if the intention is to carry out an SQL query involving attribute tables from two layers. I am still trying to figure out when does one want to use the Merge Shapefiles To One alternative...my head too lazy to think because it feels like a holiday today after the General Election.



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