The time of day (and possibly the date) changes for a vehicle when it crosses a time zone. If time zones are not configured on a network dataset that spans multiple time zones, time-of-day values in an analysis can be a source of confusion. Moreover, traffic-enabled network datasets can return incorrect travel times, and live-traffic network datasets can render traffic conditions for the wrong time if time zones are ignored. To avoid these problems, you can add an attribute to your network dataset to manage time zones.
This topic explains why configuring time zones on your network dataset may be necessary, and describes how to configure a time zone attribute.
Configuring a time zone attribute on a live-traffic enabled network dataset is always required; however, it isn't always necessary to configure a time zone attribute on network datasets that don't support live traffic. For example, if a network dataset that doesn't support live traffic falls entirely within a single time zone, you don't need to configure time zones. Also, configuring time zones is not necessary if you never perform network analyses using a time-based impedance with a start time.
Time zones and network analysis
To better understand why it is critical to set up a time zone attribute on a traffic-enabled network dataset that spans multiple time zones, assume that at 8:38 a.m. a route analysis traverses two adjacent edges, starting from one edge in the mountain time zone and continuing along another in the Pacific time zone. If a time zone attribute is not configured, the network dataset will ignore the time differential and retrieve the edges' travel times based on only one time zone. This means that instead of retrieving the travel time for the edge in the Pacific time zone for 7:38 a.m., it could retrieve the travel time for 8:38 a.m. or possibly some other time of the day, depending on the default time zone.
If time zones are configured properly, however, the cost of the edge in the mountain time zone is evaluated for 8:38 a.m. local time and the edge in the Pacific time zone is correctly evaluated for 7:38 a.m. local time. The accuracy of travel times in a traffic-enabled network dataset is thus maintained. Also, directions show time zone changes.
Regardless of whether a network dataset that spans multiple time zones is traffic enabled, configuring a time zone attribute makes it easier to enter and interpret time-of-day properties—such as time windows and arrival or departure times—because their time values always refer to local time. For example, assume you add two stops—one in the eastern time zone and another in the central time zone—and want to set both their time windows to 8:00 a.m. to 9:00 a.m. local time. If time zones aren't configured, you would have to manually convert one or both of the time window values to the default time zone. Alternatively, when time zones are configured on the network dataset, the times you enter are automatically set to the local time of the underlying edge, and Network Analyst manages the time conversions internally.
How network datasets handle time zones
Time zones have a temporal offset with respect to Coordinated Universal Time (UTC). Local rules specify what the UTC offset should be, whether daylight saving time is observed, and, if it is, the offset and date ranges for daylight saving. These rules can change frequently; keeping track of all current and past rules is a difficult task. Fortunately, later versions of Windows operating systems manage this by delivering any time zone changes in the world to your computer through Windows updates. The time zones and their rules are stored in the Windows registry.
The ArcGIS Network Analyst extension retrieves the UTC offsets and daylight saving time rules for time zones from the Windows registry. The conceptual diagram below shows a general overview of how this works.
A TimeZoneID field on the edge source features indicates the time zone the features are in. The TimeZoneID value is a foreign key to a time zone table, which resides in the same workspace as the network dataset and stores a list of time zones. The MSTimeZone field in the time zone table is also a foreign key, but to an entry in the Windows registry. (It's more common to see integer values as identifiers and foreign keys; however, the registry uses text to identify time zones.) The registry provides information to Network Analyst about the UTC offset and any date ranges for daylight saving time.
As shown in the graphic, you need a time zones table and a TimeZoneID field on your edge source feature classes before you can configure time zones on the network dataset. Once you have these components, you can create a time zone network attribute.
The following properties can be configured for the time zone attribute:
- Add Time Zone Attribute—Check this check box to use time zones while doing analysis.
- Time Zone Table—The drop-down list contains time zone tables that reside in the current network dataset's workspace. The time zone table is identified by the special field (MSTimeZone) in the table.
- Evaluators—Each attribute defined in the network must provide values for each source and direction (along and against for edges) participating in the network. An evaluator assigns values for the attribute of each source and travel direction, and a default evaluator for each element is used for those sources and directions that do not have an assigned evaluator for an attribute.
Configure the time zone attribute
To perform an analysis using time zones, the attribute needs to be configured on a network dataset. Follow the steps below to configure the time zone attribute:
- Access network attributes on the Network Dataset Properties dialog box.
- Click the Time Zone tab.
- Check the Add Time Zone Attribute check box.
- From the Time Zone Table drop-down list, choose the time zone table you want to use.
- In the Evaluators section, assign an evaluator to the source features.
- Click OK.
The time zone attribute is configured and saved to the network dataset.
Wakati wa siku (na labda tarehe) hubadilika kwa gari linapovuka eneo la wakati. Kama maeneo ya muda si umeboreshwa juu ya mtandao dataset kwamba spans maeneo mengi ya muda, wakati wa siku maadili katika uchambuzi inaweza kuwa chanzo cha kuchanganyikiwa. Zaidi ya hayo, trafiki-kuwezesha mtandao datasets inaweza kurudi makosa safari nyakati, na kuishi-traffic mtandao datasets inaweza kutoa hali ya trafiki kwa wakati mbaya kama maeneo ya muda ni kupuuzwa. Ili kuepuka matatizo haya, unaweza kuongeza sifa kwa mtandao wako dataset kusimamia maeneo ya muda. Mada hii inaelezea kwa nini kuanzisha maeneo ya muda kwenye seti yako ya data ya mtandao inaweza kuwa muhimu, na inaelezea jinsi ya kuanzisha sifa ya eneo la muda. Kuanzisha sifa ya eneo la muda kwenye seti ya data ya mtandao iliyowezesha trafiki ya moja kwa moja ni lazima kila wakati; hata hivyo, sio lazima kila wakati kuanzisha sifa ya eneo la muda kwenye seti za data za mtandao ambazo hazitegemezi trafiki ya moja kwa moja. Kwa mfano, kama mtandao dataset ambayo haina msaada kuishi trafiki iko kabisa ndani ya eneo moja la wakati, huna haja ya configure maeneo ya muda. Pia, Configuring maeneo ya muda si muhimu kama wewe kamwe kufanya uchambuzi wa mtandao kwa kutumia muda-msingi impedance na wakati wa kuanza. Ili kuelewa vizuri kwa nini ni muhimu kuanzisha sifa ya eneo la muda kwenye seti ya data ya mtandao iliyowezesha trafiki ambayo inashughulikia maeneo mengi ya wakati, fikiria kwamba saa 8:38 asubuhi, uchambuzi wa njia hupita kingo mbili zilizo karibu, kuanzia kingo moja katika eneo la wakati wa mlima na kuendelea kwenye kingo nyingine katika eneo la wakati wa Pasifiki. Kama sifa ya eneo la muda si umeboreshwa, mtandao dataset itapuuza tofauti ya muda na kupata kingo 'wakati wa kusafiri kulingana na eneo moja tu la muda. Hii inamaanisha kwamba badala ya kupata wakati wa kusafiri kwa makali katika eneo la wakati wa Pasifiki kwa 7:38 asubuhi, inaweza kupata wakati wa kusafiri kwa 8:38 asubuhi au wakati mwingine wa siku, kulingana na eneo la wakati wa default. Wakati wa eneo la muda, wakati wa eneo la wakati wa mlima ni 8:38 GMT, wakati wa eneo la muda wa Pasifiki ni 7:38 GMT. Usahihi wa muda wa kusafiri katika mtandao wa trafiki-kuwezesha dataset ni hivyo kudumishwa. Pia, mwelekeo huonyesha mabadiliko ya eneo la wakati. Bila kujali kama mtandao dataset ambayo spans maeneo mengi ya muda ni trafiki kuwezeshwa, Configuring eneo la muda sifa inafanya kuwa rahisi kuingia na kutafsiri wakati wa siku mali kama vile muda madirisha na kuwasili au kuondoka nyakati kwa sababu thamani yao ya muda daima rejea muda wa ndani. Kwa mfano, kudhani wewe kuongeza vituo viwili - moja katika mashariki ya muda zone na nyingine katika kituo cha muda zone - na wanataka kuweka wote madirisha yao ya muda kwa 8:00 a.m. kwa 9:00 a.m. wakati wa ndani. Kama maeneo ya muda si umebadilishwa, ingekuwa na manually kubadilisha moja au wote wawili wa maadili ya dirisha wakati kwa eneo la muda default. Vinginevyo, wakati maeneo ya muda ni umeboreshwa juu ya mtandao dataset, nyakati wewe kuingia ni moja kwa moja kuweka kwa muda wa ndani ya makali ya msingi, na Network Analyst inasimamia muda wa uongofu ndani. Jinsi data seti ya mtandao kushughulikia maeneo ya muda maeneo ya muda kuwa na muda offset kuhusiana na Coordinated Universal Time (UTC). Sheria za eneo husema ni nini offset ya UTC inapaswa kuwa, kama wakati wa majira ya joto unazingatiwa, na, ikiwa ni, offset na tarehe mbalimbali kwa ajili ya majira ya joto. Kanuni hizi zinaweza kubadilika mara kwa mara; kufuatilia sheria zote za sasa na za zamani ni kazi ngumu. Kwa bahati nzuri, matoleo ya baadaye ya mifumo ya uendeshaji ya Windows kusimamia hii kwa kutoa mabadiliko yoyote ya eneo la wakati katika dunia kwa kompyuta yako kupitia updates Windows. Vituo vya wakati na sheria zao ni kuhifadhiwa katika Windows Usajili. ArcGIS Network Analyst Extension hupata UTC offsets na sheria za muda wa kuokoa mwanga wa mchana kwa maeneo ya wakati kutoka kwa Usajili wa Windows. Mchoro wa dhana hapa chini inaonyesha muhtasari wa jumla wa jinsi hii kazi. TimeZoneID shamba juu ya kipengele chanzo makali inaonyesha eneo la muda kipengele ni katika. TimeZoneID ni muhimu ya kigeni kwa meza ya eneo la muda, ambayo inakaa katika nafasi ya kazi sawa na data ya mtandao na kuhifadhi orodha ya maeneo ya muda. MSTimeZone uwanja katika meza ya eneo la muda pia ni ufunguo wa kigeni, lakini kwa kuingia katika Windows Usajili. (Ni kawaida zaidi kuona maadili integer kama vitambulisho na funguo za kigeni; hata hivyo, usajili hutumia maandishi kutambua maeneo ya muda.) Usajili hutoa habari kwa Network Analyst kuhusu UTC offset na yoyote tarehe mbalimbali kwa ajili ya muda wa majira ya joto. Kama inavyoonyeshwa katika picha, unahitaji meza ya maeneo ya wakati na uwanja wa TimeZoneID kwenye madarasa yako ya kipengele cha chanzo cha makali kabla ya kuweza kusanidi maeneo ya wakati kwenye seti ya data ya mtandao. Mara baada ya kuwa na vipengele hivi, unaweza kuunda sifa ya mtandao wa eneo la muda. Mali zifuatazo inaweza kuwa umeboreshwa kwa ajili ya sifa ya eneo la muda: - Kuongeza eneo la muda sifa <unk> Check sanduku hili kutumia maeneo ya muda wakati wa kufanya uchambuzi. - Zoni ya Muda Jedwali<unk>Orodha ya kushuka chini ina meza za eneo la wakati ambazo ziko katika eneo la kazi la seti ya data ya mtandao wa sasa. Jedwali la eneo la wakati hutambuliwa na uwanja maalum (MSTimeZone) katika jedwali. - Evaluators<unk>Kila sifa maalum katika mtandao lazima kutoa maadili kwa kila chanzo na mwelekeo (pamoja na dhidi ya kingo) kushiriki katika mtandao. Mtihani hutumia thamani kwa sifa ya kila chanzo na mwelekeo wa kusafiri, na mtihani wa default kwa kila kipengele hutumiwa kwa vyanzo na mwelekeo ambao hauna mtihani uliopewa sifa. Configure eneo la muda sifa Kufanya uchambuzi kwa kutumia maeneo ya muda, sifa inahitaji kuwa umeboreshwa juu ya mtandao dataset. Fuata hatua hapa chini ili kusanidi sifa ya eneo la wakati: - Upatikanaji wa sifa za mtandao kwenye sanduku la mazungumzo la Network Dataset Properties. - Bonyeza tab ya Eneo la Wakati. - Angalia kuongeza wakati eneo sifa sanduku la kuangalia. - Kutoka orodha ya chini ya Jedwali la Eneo la Wakati, chagua jedwali la eneo la wakati unayotaka kutumia. - Katika sehemu ya Evaluators, kumpa mtihani kwa vipengele chanzo. - Bonyeza OK. sifa ya eneo la muda ni umeboreshwa na kuhifadhiwa kwa mtandao dataset.